Food Safety Risks Associated with Prawns Consumed in ...

Food Safety Risks Associated with Prawns Consumed in

Australia

Seafood CRC Project: 2009/787

Prawn Market Access Defenders

John Sumner

September 2011

1

Foreword

In 2009 The Australian Council of Prawn Fisheries (ACPF) held a meeting in Brisbane to

discuss and plan future research priorities; food safety was identified as a priority for the

industry at this meeting.

Subsequently, the SARDI Food Safety group were engaged by the Australian Seafood

Cooperative Research Centre (ASCRC) and the ACPF to undertake a project to identify food

safety risks posed by potential hazards in prawns and if necessary, prioritise opportunities for

reducing risk through targeted initiatives. This report presents the findings of the project.

The report scientifically evaluated the human health impact of chemical and microbial

hazards associated with prawns. Risk ratings indicate a VERY LOW risk of human illness

associated with the consumption of prawns produced domestically, imported prawns and

exported prawns. This finding is consistent with the public health record which shows few

reports of illness related to the consumption of prawns that have been handled appropriately.

The report was favourably peer reviewed by Dr Iddya Karunasagar (United Nations Food and

Agricultural Organisation) and Dr Alan Reilly (Food Safety Authority of Ireland)

(Appendix 1).

The scientific findings contained in this report may assist negotiations for improved trade

access conditions into domestic and overseas markets, and risk commensurate testing

requirements for retail outlets.

SARDI gratefully acknowledges Dr John Sumner for authorship of the report, members of

the project steering group for valuable input and advice (Jayne Gallagher, Lynda Feazey, Dr

Andrew Pointon, Dr Cath McLeod and Graeme Stewart) and the contributions of Dr Andreas

Kiermeier and Jo Slade. We also thank the ASCRC and ACPF for their financial support.

2

Table of Contents

ABBREVIATIONS ....................................................................................................................... 3

EXECUTIVE SUMMARY .............................................................................................................. 5

BACKGROUND ........................................................................................................................... 8

TOR 1: HAZARD IDENTIFICATION – AUSTRALIAN PRAWNS IN INTERNATIONAL TRADE ......... 11

Approach ............................................................................................................................ 11

National Risk Validation Project (NRVP) and OzFoodNet Food Poisoning Data ............ 11

FSANZ Recalls .................................................................................................................. 13

EU Alerts for Crustaceans ................................................................................................. 13

AQIS Sampling Program for Imported Prawns ................................................................. 15

Hazard Identification Summary ......................................................................................... 17

References .......................................................................................................................... 17

TOR 2: HAZARD SHEETS FOR IDENTIFIED HAZARDS .............................................................. 18

Vibrio cholerae .................................................................................................................. 18

Vibrio parahaemolyticus .................................................................................................... 36

Salmonella .......................................................................................................................... 51

Hepatitis A (HAV) ............................................................................................................. 58

Chloramphenicol ................................................................................................................ 62

Sulphite .............................................................................................................................. 64

Nitrofurans ......................................................................................................................... 66

Cadmium ............................................................................................................................ 68

TOR 3: RISK ASSESSMENT OF IDENTIFIED HAZARDS .............................................................. 71

3.1 Qualitative Risk Assessment Tool ............................................................................. 71

3.2 Semi-Quantitative Risk Assessment Tool - Risk Ranger .......................................... 72

3.3 Identified Hazards ...................................................................................................... 74

References .......................................................................................................................... 74

TOR 4: RISK ASSESSMENT OF HAZARD:PRODUCT PAIRINGS .................................................. 75

4.1 Risk Assessment: Vibrio cholerae ............................................................................. 75

4.2 Risk Assessment: Vibrio parahaemolyticus .............................................................. 81

4.3 Risk Assessment: Salmonella .................................................................................... 87

4.4 Risk Assessment of Chemical Hazards ...................................................................... 93

APPENDIX 1: REVIEW REPORT ON ‘FOOD SAFETY RISKS ASSOCIATED WITH PRAWNS

CONSUMED IN AUSTRALIA’ ................................................................................................ 95

Important Notice

Although SARDI has taken all reasonable care in preparing this report, neither SARDI nor its

officers accepts any liability from the interpretation or use of the information set out in the

document. Information contained in this document is subject to change without notice.

3

Abbreviations

ABARE Australian Bureau of Agricultural and Resource Economics

ADI Acceptable Daily Intake

AHD 1-aminohydantoin (Nitrofurantoin)

AMOZ 3-amino-5- morpholinomethyl-1,3-oxazolidin (Furaltadone)

AOZ 3-amino-oxazolidinone (Furazolidone)

APFC Australian Prawn Fisheries Council

AQIS Australian Quarantine Inspection Service

ASCRC Australian Seafood Cooperative Research Centre

CAP Chloramphenical

CCP Critical Control Point

CSIRO Commonwealth Scientific and Industrial Research Organisation

EFSA European Food Safety Authority

EU European Union

FAO Food and Agriculture Organization

FDA Food and Drug Administration (US)

FSA Food Science Australia

FSANZ Food Standards Australia New Zealand

GHP Good Hygiene Practices

GMP Good Manufacturing Practices

HACCP Hazard Analysis and Critical Control Point

HAV Hepatitis A

ICMSF International Commission on Microbiological Specifications for Foods

IQF Individually quick frozen

JECFA Joint Expert Committee on Food Additives (FAO/WHO)

ML Maximum Level

MRL Maximum Residue Limit

NACMCF National Advisory Committee on Microbiological Criteria for Foods

NEPSS National Enteric Pathogens Surveillance Scheme

NoV Norovirus

NRVP National Risk Validation Program

PFGE Pulsed-Field Gel Electrophoresis

PTWI Provisional Tolerable Weekly Intake

SARDI South Australian Research and Development Institute

4

SEM Semicarbazide (Nitrofurazone)

SSOP Sanitation Standard Operating Procedure

TOR Term of Reference

VBNC Viable but non-culturable

WHO World Health Organization

5

Executive Summary

The Project

The Australian Prawn Fisheries Council (APFC) and the Australian Seafood Cooperative

Research Centre (CRC) commissioned SARDI to undertake a food safety risk rating of

prawns consumed in Australia.

The terms of references (TORs) for this study are to:

1. Undertake a hazard identification for imported and domestic prawns

2. Construct hazard sheets for each identified hazard

3. Undertake a qualitative risk ranking and where data permit, a semi-quantitative

ranking using Risk Ranger

4. Write a draft report and circulate to reference group (including technical

information as appendices)

5. Prepare a final report

6. Arrange a stakeholder workshop to discuss report.

This report covers TORs 1-4 above and focuses on hazards in:

Prawns produced domestically

Imported prawns

Export prawns.

TOR 1: Hazard Identification

Food safety hazards in prawns in international trade have been identified by interrogating

the following data sources:

National Risk Validation Project

OzFoodNet food poisoning data

FSANZ recalls

European Union (EU) alerts for crustaceans

AQIS sampling program for imported prawns

EU Market Access Program

For prawns caught/harvested in Australia:

The sole perceived hazard according to EU authorities is cadmium.

There have been no instances of illness caused by prawns produced by the

domestic industry; consideration of risks from pathogenic bacteria in domestically-

produced prawns did not pass the Hazard Identification stage of risk assessment.

For imported prawns a range of chemical and microbiological hazards has been

identified:

Nitrofurans

Sulphites

Chloramphenicol

Cadmium

6

Vibrio parahaemolyticus

Vibrio cholerae

Salmonella

Hepatitis A

TOR 2: Construct Hazard Sheets for each Hazard

Hazard sheets have been constructed which, in the case of microbiological hazards,

update those used for the National Seafood Risk Assessment of 2001 commissioned by

Seafood Services Australia.

The update was facilitated greatly by material available from the joint FAO-WHO expert

panel on Vibrios in Seafoods and the FAO expert consultation on The application of

biosecurity measures to control Salmonella contamination in sustainable aquaculture.

TOR 3: Undertake Risk Ranking

Risk ratings were carried out for each of these perceived hazards using a qualitative tool

based on one developed by CSIRO and where sufficient data were available, a semi-

quantitative tool, Risk Ranger:

Biological Hazards Risk Assessment Carried Out

Vibrio parahaemolyticus Qualitative Semi-quantitative

Vibrio cholerae Qualitative Semi-quantitative

Salmonella Qualitative Semi-quantitative

Hepatitis A* None

Chemical Hazards

Sulphite Qualitative

Cadmium Qualitative

Chloramphenicol Qualitative

Nitrofurans Qualitative

* There was insufficient information to undertake even a qualitative risk assessment

The estimated risk of illness caused by pathogens in imported prawns – less than one

illness/annum - is in line with observed public health data.

For several reasons, achieving a useful assessment of risk from ingesting chemicals

contained in prawns is difficult:

There are no recorded cases of illness associated with the hazard:product pairing.

Chronic exposure over many years may be required for adverse reaction (e.g.

cadmium intake and kidney disease).

Risk of exposure is considered dose-independent e.g. any dose of chloramphenicol

and nitrofurans is considered by some authorities (EU) to be disease-causing at any

dose.

7

The application of ‘zero tolerance’, with its implied ‘zero risk’, effectively

precludes any application of probability to an adverse event occurring.

The foregoing has led some authorities (e.g. EU) to set levels based on the ‘precautionary

principle’, which is a concept diametrically opposed to risk assessment.

As part of an EU Market Access Program, the South Australian Research and

Development Institute (SARDI) undertook residue testing of prawns in conjunction with

the Australian Prawn Farmers Association (APFA). All samples of prawns from six

prawn farms had levels below the laboratory limit of detection for chloramphenicol

(0.19µg/kg), AHD, AMOZ and AOZ (0.2µg/kg) and SEM (0.4µg/kg).

Risk ratings were Very Low for sulphite, chloramphenicol, nitrofurans and cadmium in

prawns.

Risk ratings of microbiological hazards in prawns imported to Australia

Hazard Product Qualitative

Assessment

Semi-quantitative

Assessment

Risk

Rating

Estimated

Illnesses

V. cholerae Raw prawns Very low 28 1.7/decade

Prawns cooked at the

plant and eaten without

further heat treatment

Very low 0 0

Prawns cooked

immediately before

consumption

Very low 0 0

V. parahaemolyticus Raw prawns Very low 22 1.5/decade




Very low 0 0

Prawns cooked

immediately before

consumption

Very low 0 0

Salmonella Raw prawns Very low 16 1.5/decade




Very low 0 0

Prawns cooked

immediately before

consumption

Very low 0 0

Conclusions

The present project ratings are in line with public health data linking prawns with illness.

Despite being a huge commodity in international trade there are few reports of illness where

handling standards are maintained according to those contained in the Food Standards Codes

of importing countries.

8

Background

As indicated in Table 1, Australia typically produces around 20,000 t of prawns annually, of

which around 25% is exported (based on ABARE statistics for the years 2005-2008).

Domestic consumption is augmented by around 20,000 t of imported prawns, with Vietnam,

Thailand and China accounting for around 75% of imports (Table 2). Japan is by far the

largest single export market, though, as indicated in Table 3, exports fell significantly

between 2005 and 2008.

The data presented in Tables 1-3 serve to inform the exposure Australian and overseas

consumers face from consumption of prawns. Under TOR 1, these hazards are identified for

prawns produced in and imported to Australia. This report aims to integrate exposure to

specific hazards with each hazard’s characteristics to produce a risk ranking.

As such, this report will update previous risk rankings for microbial hazards published in the

national seafood risk assessment (Seafood Services Australia, 2001) and in Sumner and Ross

(2002). Two risk assessments relevant to the present study were made:

Enterics (non-Vibrio) in cooked crustaceans

Vibrios in molluscs and crustaceans

In the former, the researchers noted that there had been only two recorded outbreaks of food

poisoning, both due to Shigella spp (Table 4). In these outbreaks imported Asian prawns were

incriminated in the Dutch incident, while in the UK incident the importing country was not

identified. The shigelloses were attributed to post-process contamination, possibly involving

a food handler in the carrier state, or the use of contaminated water. No recorded outbreaks

were found for other enteric pathogens such as Salmonella, Escherichia coli, Campylobacter

or Yersinia.

In the 2001 risk assessment referred to above, cooked prawns were imported from Asian

countries and comprised aquaculture prawns, almost exclusively Penaeus monodon. Using a

semi-quantitative tool, Risk Ranger, a ranking of 31 was established for enterics in cooked

prawns with a prediction of five illnesses per annum, almost all coming from vulnerable

consumers (young, old, pregnant and immunocompromised).

It was noted that there had been two large outbreaks of V. parahaemolyticus gastroenteritis in

Australia linked with consumption of prawns (Kraa, 1995). In 1990 an outbreak affecting

more than 100 people, one of whom died, was linked to fresh, cooked prawns from

Indonesia. In 1992 there were two outbreaks affecting more than 50 people linked to the same

wholesale supplier of cooked prawns. The Risk Ranger ranking for V. parahaemolyticus in

imported cooked prawns was 37, with six illnesses predicted per annum. Similar ranking and

illnesses were predicted for vulnerable consumers consuming cooked imported prawns

contaminated with V. cholerae.

It should be noted that, in the decade following the first risk assessment, the body of

information has increased greatly. The FAO and WHO have undertaken a series of risk

assessments on Vibrios in Seafoods, while FAO has examined measures to control

Salmonella contamination in aquaculture products. These, and other sources, will be used in

the present update of hazards and risks associated with Australian and imported prawns.

9

Table 1: Summary statistics Australia’s prawn industry 2005-2008 (after ABARE statistics)

Volume (t) Value ($,000) Price ($/kg)

2005-06 2006-07 2007-08 2005-06 2006-07 2007-08 2005-06 2006-07 2007-08

Exports 8744 6376 4916 133923 93563 68624 15.32 14.67 13.96

Imports 23165 26016 18731 201351 246387 166646 8.69 9.47 8.90

Production 20046 17490 19342 255040 222232 223339 12.72 12.71 11.55

Table 2: Main sources of prawns imported into Australia (after ABARE statistics)


2005-06 2006-07 2007-08 2005-06 2006-07 2007-08 2005-06 2006-07 2007-08

Indonesia 1094 686 197 8508 5675 1841 7.78 8.27 9.35

India 2459 2000 1084 25451 24420 12208 10.35 12.21 11.26

China 4465 8469 5486 29417 62120 36737 6.59 7.33 6.70

Thailand 6106 5503 4694 45968 48228 38613 7.53 8.76 8.23

Vietnam 6855 7229 4856 72307 85791 52951 10.55 11.87 10.90

Other 2132 2128 2414 19700 20153 24296 9.24 9.47 10.06

Table 3: Main destinations for export of prawns from Australia 2005-2008 (after ABARE statistics)


2005-06 2006-07 2007-08 2005-06 2006-07 2007-08 2005-06 2006-07 2007-08

Japan 3116 2442 1792 59665 45446 31848 19.15 18.61 17.77

China 1124 1101 529 11999 11277 4808 10.68 10.24 9.09

Spain 1434 877 331 18972 10233 3424 13.23 11.67 10.34

Hong Kong 401 413 425 5758 5960 5959 14.36 14.43 14.02

Vietnam 548 458 317 7607 5113 3868 13.88 11.16 12.20

Table 4: Documented outbreaks of illness from cooked prawns with enteric pathogens

Date Country Organism Impact Reference

1983-4 Holland Shigella flexneri 14 dead van Spreekens (1985)

1992 UK Shigella sonnei 119 ill Anon. (1992)

10

Terms of Reference

The terms of references (TORs) for this study are:

1. Undertake a hazard identification for imported and domestic prawns.

2. Construct hazard sheets for each identified hazard.

3. Undertake a qualitative risk ranking and where data permit, a semi-quantitative ranking

using Risk Ranger.

4. Write draft report and circulate to reference group (including technical information as

appendices).

5. Prepare a final report.

6. Arrange a stakeholder workshop to discuss report.

References

Anonymous. 1992. An outbreak of Shigella sonnei infection. Communicable Disease Report

CDR Weekly Feb 21, 2(8):33.

Kraa, E. 1995. Surveillance and epidemiology of foodborne illness in NSW, Australia. Food

Australia 47(9):418-423.

Seafood Services Australia. 2001. Seafood Services Australia: Seafood food safety risk

assessment – phase 2. FRDC project No. 2000/245.

Sumner, J. and Ross, T. 2002. A semi-quantitative seafood safety risk assessment.

International Journal of Food Microbiology 77, 55-59.

van Spreekens, K. 1985. A methodology for the isolation of Shigella flexneri from imported

Asian prawns. Microbiologie Aliments Nutrition, 3(1):63-71.

11

TOR 1: Hazard Identification – Australian Prawns in International Trade

Approach

A number of sources have been explored in identifying food safety hazards in prawns in

international trade. The following data sources have been interrogated:

1. National Risk Validation Project

2. OzFoodNet food poisoning data

3. FSANZ recalls

4. European Union (EU) alerts for crustaceans

5. AQIS sampling program for imported prawns

6. SARDI EU market access program

Together, the data sources inform on hazards encountered in:

Prawns produced domestically

Imported prawns

Prawns exported

National Risk Validation Project (NRVP) and OzFoodNet Food Poisoning Data

Food Science Australia and Minter Ellison Consulting published the NRVP in 2002 and

assembled an exhaustive database of food poisonings in Australia over the period 1990-2001.

In 2001, OzFoodNet began collating data on food poisoning outbreaks on a state-by-state

basis.

The NRVP and OzFoodNet data on ten outbreaks of food poisoning following consumption

of prawns over the 21-year period 1990-2010 are presented in Table 5. During the period,

more than 230 individuals became sufficiently ill to enter the medical system and become

registered cases; one died.

Aetiological agents identified as hazards are, in order of prevalence:

V. parahaemolyticus

Hepatitis A

V. cholerae non 01, non 139

S. typhi

12

Table 5: Food poisoning outbreaks due to the consumption of prawns in Australia 1990-2010 (after NRVP and OzFoodNet)

Source Hazard Country Cases (deaths) Year Reference

Retail V. parahaemolyticus Indonesia. 27 1990 NSW Health

Caterer V. parahaemolyticus Indonesia 100 (1) 1990 NSW Health; Kraa, 1995

Importer V. parahaemolyticus Indonesia >50 1992 Kraa, 1995

Eating est. S. typhi Thailand 4 1995-1996 NSW Health

Eating est. Hepatitis A Burma 23 1997 NSW Health

Eating est. Hepatitis A Burma 17 1997 Anonymous, 1997

Eating est. V. cholerae non 01, non 139* Not recorded 10 1999 OzFoodNet

Eating est. Hepatitis A Not recorded 2 2003 OzFoodNet

Eating est. Unknown Not recorded 2 2009 OzFoodNet

* Red claw crayfish

13

FSANZ Recalls

Over the period 2000-2011, FSANZ registered five recalls of prawn products (Table 6), from

which may be added non-typhoidal serovars of Salmonella to the list of hazards.

Table 6: Recalls of prawn products registered with FSANZ (1999-2011)

Year Product Format Hazard

1999 P. monodon Cooked, peeled V. cholerae

2004 P. monodon Cooked S. infantis

2005 P. vannamei Cooked Microbial contamination

2007 P. monodon Cooked Metal

2007 P. monodon Raw, peeled Labelling (labelled as cooked)

EU Alerts for Crustaceans

Hazards in crustaceans registered by the EU rapid alert system are listed in Table 7. Over the

period 1980-2010 (though preponderantly 1998-2010) the majority of alerts have been for

chemicals perceived as hazards: nitrofurans, sulphite, chloramphenicol and cadmium, with a

minority being due to vibrios and Salmonella.

Countries responsible for triggering alerts from crustaceans imported to the EU are listed in

Table 8. The majority of alerts stem from Asian imports, reflecting the prevalence of Asian

prawns in international trade. Alerts from French product are overwhelmingly linked with

trade in crabs while those from Australian prawns are linked with cadmium.

An appraisal of microbiological hazards prompting alerts was undertaken over the period

1995-2010. Over this time there were 230 alerts, of which 200 occurred during 2000-2005

(Table 9); 209/230 were linked with prawns and the remainder with crabs and lobsters (Table

10). It cannot be determined why alerts have decreased so markedly post-2005.

Among microbiological hazards causing alerts, the vast majority were due to

V. parahaemolyticus and V. cholerae (Table 11), with Malaysian, Indian, Bangladeshi and

Thai product being implicated on 50, 31, 24 and 22 occasions, respectively (Table 12).

Table 7: Alerts triggered from prawn imports to the EU (1980-2010)

Hazard Number of alerts

Nitrofurans 377

Sulphite 295

Chloramphenicol 163

Cadmium 133

V. parahaemolyticus 112

Salmonella 66

V. cholerae 50

Other 299

Total 1495

14

Table 8: Country of origin of prawns triggering alerts in the EU (1980-2010)

Country Number of Alerts Main Cause

India 215 Nitrofurans

Bangladesh 161 Nitrofurans

China 135 Chloramphenicol, nitrofurans

Vietnam 123 Chloramphenicol, nitrofurans, vibrios

France 120 Sulphite, cadmium (crabs)

Thailand 87 Nitrofurans

Malaysia 71 V. parahaemolyticus

Indonesia 65 Nitrofurans

Brazil 62 Sulphite

Australia 39 Cadmium

Ecuador 39 Vibrios

Other 378

Total 1495

Table 9: EU alerts due to microbiological hazards (1995-2010)

Year Number of Alerts

1995 1

1996 0

1997 3

1998 10

1999 20

2000 33

2001 40

2002 35

2003 17

2004 37

2005 18

2006 4

2007 2

2008 8

2009 1

2010 1

Total 230

15

Table 10: EU alerts according to crustacean products

Product Number of Alerts

Crab 6

Crayfish 15

Shrimp 209

Total 230

Table 11: Microbiological hazards triggering EU alerts from crustaceans

Hazard Number of Alerts

B. cereus 1

Salmonella 6

S. aureus 1

Clostridium 1

V. parahaemolyticus 137

V. cholerae 98

Vibrios 8

V. alginolyticus 5

V. vulnificus 4

V. fluvialis 1

V. mimicus 1

Total 263

Table 12: Countries of origin causing EU alerts due to microbiological hazards

Country of origin Number of Alerts

Malaysia 50

India 31

Bangladesh 24

Thailand 22

China 19

Vietnam 18

Indonesia 14

Ecuador 13

Brazil 10

Others 29

Total 230

AQIS Sampling Program for Imported Prawns

Over the six year period 2005-2010, AQIS arranged for 5,247 tests on consignments of

imported prawns, of which 94 (1.79%) failed acceptance criteria (Table 13).

16

Table 13: Sampling frequency and rejection rate for prawns imported into Australia (2005-2010)

Year Total Tests Failed Tests Percentage Failure

2005 450 8 1.78

2006 1577 49 3.11

2007 1570 33 2.10

2008 434 1 0.23

2009 530 2 0.38

2010 686 1 0.15

Total 5247 94 1.79

The vast majority of positive tests (82.7%) were in 2006 and 2007, when consignments from

China and India were responsible for 72.3% of all positive tests (Table 14).

Hazards which caused rejection are listed in Table 15 from which it can be seen that chemical

hazards comprise 84% of rejections, with nitrofurans accounting for 78.5% of chemical

rejections; China and India together supplied 87% of consignments rejected for failing

chemical criteria.

Microbiological rejections were due to presence of V. cholerae (13/93) and for high Standard

Plate Count (2/94).

Table 14: Country of origin of rejected consignments (2005-2010)

Year Vietnam Indonesia Thailand Singapore China India Malaysia Total

2005 2 2 3 1 0 0 0 8

2006 3 0 0 0 29 17 0 49

2007 0 0 8 0 12 10 3 33

2008 0 0 1 0 0 0 0 1

2009 0 1 0 0 1 0 0 2

2010 0 0 0 0 0 0 1 1

Total 5 3 12 1 42 27 4 94

Table 15: Country of origin and cause of rejection of prawns imported into Australia (2005-2010)

Vietnam Thailand Singapore China India Indonesia Malaysia Total

Cloramphenicol 2 2 1 5

Fluoroquinones 8 8

Nitrofurans 36 26 62

Standard Plate

Count

2 2

Sulphur dioxide 3 1 4

Vibrio cholerae 2 6 1 4 13

Total 5 12 1 42 27 3 4 94

17

Hazard Identification Summary

For consumers of Australian prawns the sole perceived hazard according to EU authorities is

cadmium. By contrast, according to perceptions of risk by AQIS (on advice from FSANZ),

imported prawns present a wide range of chemical and microbiological hazards: nitrofurans,

sulphite, chloramphenicol, cadmium, V. parahaemolyticus, V. cholerae, Salmonella and

Hepatitis A.

It should be noted that:

(i) Human illnesses are generally caused by strains of V. parahaemolyticus that are either

tdh+ or rarely, trh+ and strains possessing these attributes constitute a very small

proportion, if at all, of the natural population associated with the environment and

seafood.

(ii) Public health risk should be equated with the natural presence of this organism and

with the large number of import alerts that are triggered without further testing to

determine whether the isolates are, in fact, toxigenic.

This factor is developed in Section 3 of the Hazard Sheet for V. parahaemolyticus.

References

Anonymous. 1997. Hepatitis A outbreak in New South Wales. Communicable Diseases

Intelligence 21(13), 17.


Australia 47(9), 418-423.

18

TOR 2: Hazard Sheets for Identified Hazards

Vibrio cholerae

1. Hazard Identification

Outbreaks of cholera have been associated with consumption of seafood including oysters,

crabs and prawns (Oliver & Kaper, 1997). In the early 1990s, there was a cholera pandemic

in South and Central America, most outbreaks occurring in Peru, where there were >400 000

cases and an estimated 4,000 deaths (Wolfe, 1992). The pandemic was not associated with

consumption of seafood produced commercially, but to contaminated water supplies used in

the preparation of a popular fermented seafood dish, ceviche.

Warm-water prawn is an important commodity in international trade with the vast majority of

production originating from developing countries (FAO, 1999), making it a very important

commodity for these countries.

The global prawn trade has responded to the major HACCP initiatives of the United States of

America (Seafood HACCP Regulation) and of the European Union (concept of ‘own checks’

and critical control points) as prerequisites for maintaining trade. Many importing countries,

including Australia, operate microbiological monitoring systems at ports of entry.

1.1 V. cholerae serovars of concern

According to the WHO definition, choleragenic V. cholerae O1 and O139 are the only

causative agents of cholera. Other serogroups (serovars) are generally termed non-O1, non-

O139 strains, are generally non-choleragenic, usually cause a milder form of gastroenteritis

than O1 and O139, and are normally associated with sporadic cases and small outbreaks

rather than with epidemics and pandemics (Kaper et al. 1995; Borroto, 1997; Desmarchelier,

1997).

The O1 serovar has three antigenic forms: Inaba, Ogawa and Hikojima, and can be classified

into two biotypes, Classical and El Tor, based on their phenotypic characteristics (Kaper et

al. 1995). Recent studies have shown that the Classical biotype strains are rarely isolated

from any part of the world (Sack et al. 2003). The choleragenic El Tor biotype strains of

V. cholerae are grouped in four major clonal groups which seem to reflect broad

demographic and epidemiological associations (Wachsmuth et al. 1994):

(i) The seventh pandemic

(ii) The U.S. Gulf Coast

(iii) Australia

(iv) Latin America (difficult to distinguish from the seventh pandemic strain and

produces a very similar PFGE pattern),

The most important virulence factor associated with V. cholerae O1 and O139 is the cholera

toxin. The ctx genes (ctxA and ctxB) encoding the production of the cholera toxin have been

sequenced and this has enabled development of DNA probes and polymerase chain reaction

(PCR) methods for detection of this gene, enabling specific detection of choleragenic

V. cholerae from seafood and water.

19

In addition to cholera toxin, choleragenic strains of V. cholerae possess the ability to adhere

to, and colonise, the small intestine (colonisation factor), which has been attributed, inter

alia, to a toxin-co-regulated pilus (TCP).

Though ctx-positive non-O1, non-O139 strains have been found, these strains often lack the

full set of virulence genes found in epidemic strains. Although ctx-positive non-O1, non-

O139 serovars of V. cholerae have been implicated in cholera-like disease, only sporadic

cases have been reported (Dalsgaard et al. 2001).

2. Exposure Assessment

2.1 Prevalence of V. cholerae O1 and O139 in prawns and water

The primary source of V. cholerae O1 and O139 is faeces of persons infected with the

organism, which reaches water supplies most often through sewage. The organism can

survive in water for long periods with an average time for a 1-log decline in cell number (t90)

between 2-4 days (Feachem et al. 1981) both in fresh- and seawater.

In Australia, V. cholerae O1 was isolated intermittently over a 22-month period from river

water that was used as an auxiliary town water supply and was implicated in a case of cholera

in 1977 (Rogers et al. 1977). However, V. cholerae O1 and O139 are confined to fresh water

and estuarine environments and there are no reports of the presence of these organisms in

offshore environments.

In the aquatic environment, there is a strong association between levels of zooplankton and

incidence of V. cholerae (Huq et al. 1983), with adhesion to chitin a major influence on its

ecology (Nalin et al. 1979). It has also been reported to attach to the hindgut of crabs (Huq et

al. 1996) and it is noted that the hindgut of crustaceans is an extension of the exoskeleton and

is lined with chitin.

Dalsgaard et al. (1995a) found that V. cholerae O1 was present in 2% (2/107) of water,

sediment and prawn samples collected from a major prawn culture area in South-east Asia.

However, subsequent testing of the isolates indicated absence of the ctx genes in both of the

O1 strains (Dalsgaard et al. 1995b). Data from India showed the presence of V. cholerae O1

in 0.2% of raw prawn (Ministry of Agriculture, India, personal communication, 2001).

However, the choleragenic status of these prawn-associated strains is unknown. Prawn

imported into Europe in early 2005 tested positive for V. cholerae; but the subsequent

detailed analysis indicated that they were non-toxigenic strains.

Crustaceans, molluscs and finfish prepared in a variety of forms have been vectors for the

transmission of V. cholerae. There is one outbreak linked to the consumption of raw prawn in

the United States of America in 1986, where the source was domestic (Lowry et al. 1989).

Another outbreak in Japan in 1978 was associated with lobsters imported from Indonesia

(IASR, 1998). There was one other cholera outbreak linked to the consumption of raw

prawns, in the Philippines in 1962, though, since the source of prawns is not known, it is not

possible to assess whether V. cholerae O1 was naturally present or there as a result of cross-

contamination after harvest (Joseph et al. 1965). The shellfish most often associated with

cholera cases are molluscan shellfish (oysters) and crabs. While oysters are consumed raw in

many countries, crabs are generally cooked, though even after boiling crabs for up to 10

minutes or steaming for up to 30 minutes, V. cholerae O1 may still retain viability (Blake et

al. 1980).

20

2.2 Occurrence of choleragenic V. cholerae O1 and O139

In wild-caught prawns there is no evidence to show that marine prawn caught by trawling in

offshore waters with salinities around 30 ppt harbour choleragenic V. cholerae O1 and O139,

these organisms occurring in waters with salinities between 0.2 and 20 ppt (Colwell & Spira,

1992). Studies conducted on freshly harvested marine prawn in India, Sri Lanka and Thailand

indicate absence of choleragenic V. cholerae (Suseela et al., 1988; Iyer et al. 1988; Fonseka,

1990; Karunasagar et al. 1990, 1992; Rattagool et al. 1990; Dalsgaard et al. 1995b).

In contrast to wild-caught, prawn aquaculture activities are generally in coastal areas and the

water source is often estuarine, allowing the introduction of V. cholerae O1 or O139 in

cholera-endemic areas. However, studies conducted in several Asian countries indicate

absence of choleragenic V. cholerae in prawn from aquaculture ponds (Reilly & Twiddy,

1992; Nayyar Ahmad et al. 1995; Bhaskar et al. 1998; Otta et al.1999; Shetty, 1999;

Darshan, 2000; Dalsgaard et al. 1995b; Gopal et al. 2005).

2.3 Growth and survival characteristics

The physicochemical factors limiting the growth of V. cholerae O1 have been summarised by

ICMSF (1996). The optimum temperature for growth is 37 C with a range of 10 to 43 C. The

pH optimum for growth is 7.6 and V. cholerae can grow in a pH range of 5.0 to 9.6. The

water activity optimum for growth is 0.984 and growth can occur between 0.970 and 0.998.

V. cholerae can grow in a salt range of 0.1–4.0% sodium chloride (NaCl), with an optimum

for growth of 0.5% NaCl.

2.4 Death or inactivation

V. cholerae O1 is highly sensitive to acidic environments and is killed within minutes in

gastric juice with pH <2.4. Therefore, normochlorohydric individuals are less susceptible to

cholera, provided the food matrix does not protect the organisms. V. cholerae O1 is also

highly sensitive to desiccation, indicating the need to use well-dried containers in product

handling to minimise the transmission of cholera. This organism is heat sensitive, with a D-

value of 2.65 minutes at 60 C (ICMSF, 1996).

Most studies indicate that, while decline occurs at refrigeration temperatures, a proportion of

the bacterial population remains viable.

2.5 Harvest, post-harvest handling and transport

Exposure assessment involves estimation of the likelihood of ingesting choleragenic

V. cholerae O1 and O139 by eating prawns contaminated with these organisms, and the

numbers of the organisms consumed. Since most of the world’s prawn production and

processing occurs in developing countries in Asia and Latin America, where cholera may be

endemic, there can be multiple modes of contamination. Therefore, a process model for

exposure assessment involves the possibility of contamination and of changes in population

during pre-harvest, harvest, post-harvest handling, retail and at household level during

preparation for consumption (Figure 1).

21

Figure 1: Production-consumption pathway for exposure assessment of V. cholerae in warm-water prawn (after FAO/WHO 2005)

Marine prawn harvested by trawling are separated from the by-catch by manual sorting and

then iced on board. Ice is generally produced using potable water in coastal ice plants and

taken on board in insulated containers. During on-board handling, contamination with

V. cholerae is possible if the person handling prawn and ice is a carrier of V. cholerae O1, or

if the ice has become contaminated with choleragenic V. cholerae. However, the use of

potable water – and in many cases the implementation of a HACCP system (as required for

products exported to many countries e.g. the United States of America, the European Union

and Australia) in the production and handling of the ice – minimises the opportunity for

faecal contamination of ice.

In cholera-endemic areas, asymptomatic carriers play an important role in transmission of the

pathogen. In fact, for water stored in households, contamination through the hand contact of

carriers has been observed as a route for transmission of cholera (Deb et al. 1986). Thus,

contamination via the hands of prawn handlers is a possible route. However, where personal

hygiene and other hygienic conditions are controlled by the implementation of GHPs and a

HACCP system in prawn processing, the likelihood of faecal contamination of prawn via

fingers becomes very low.

22

In the case of cultured prawns, faecal contamination may occur during harvest and handling

before the prawns are washed and chilled. The likelihood and level of such contamination is

unknown, although the implementation of GHPs and HACCP along the chain should mean

that this is low. Control points include dipping or washing in water, icing and packing in

plastic crates for transport by truck to the processing plant. The process of dipping or washing

may reduce the level of V. cholerae in prawns, as shown by Dinesh (1991), who

demonstrated that a one-log reduction in counts of V. cholerae was brought about when

whole prawns spiked with the organism were dipped or washed in tap water.

2.6 Processing and cooking

Post-harvest contamination with choleragenic V. cholerae will be influenced by its

concentration plus time-temperature during handling, processing and storage. Time-

temperature distributions and the effects on densities of choleragenic V. cholerae are

presented in Table 16. The study of Kolvin and Roberts (1982) indicates that V. cholerae O1

does not multiply in raw prawns. Further, the temperature of iced prawns during transport

would be <10°C, at which temperature V. cholerae O1 does not multiply.

Product intended for export is processed in facilities, including prawn trawlers, which meet

sanitary requirements for GHPs, GMPs and HACCP, where it is peeled manually or by

machine, then washed, graded, processed (e.g. heading, gutting) and in some cases cooked,

before being packed for freezing.

Cooking is undertaken for several reasons, most important of which are customer

specifications or the prevention of melanosis (black spot formation), which can occur in the

head during chilled storage. In Australia, Winkel (1997) studied the effect of cooking on

black spot formation and organoleptic quality of Penaeus monodon prawns. Winkel

established that a core temperature of 75°C was sufficient to cook the flesh, but that

prevention of black spot required a core temperature of 85°C. The time required to reach a

75°C core temperature was related to the size of prawn: almost four minutes for ‘large’ (50-

65 g) prawns and 1.5 minutes for ‘small’ (25-30 g) prawns.

As part of an Australian code of practice for farmed prawns, Sumner (1997) observed prawn

processing at six processing plants. Operators lowered each batch into ‘boiling’ water (ca

98°C) in a proportion of around 5:1 (water:prawns), a procedure which lowered the water

temperature to around 92°C. The source of heat – usually a gas-fired ring – was then

maximised and the water quickly brought to ‘boiling’ (ca 98°C), at which time the operator

activated the timing device for the process. Since overcooking results in poor organoleptic

quality and weight loss, cooking time is important. Depending on size, prawn were cooked

for between 0.5 minute (‘small’) and 1.0 minute (‘large’), then immediately plunged into an

ice-water slurry to bring an end to cooking.

23

Table 16: Time-temperature relations and their effect on concentration of choleragenic V. cholerae during processing of wild caught and aquaculture warm water prawns.

Processing Step Temp

Range (°C)

Time Concentration

change (log)

Ref

HARVEST TIME PRE-ICING

Aquaculture prawn

Wild caught prawn

15-35

10-30

0-1h

0-3h

No effect

0-1 log increase

(a) (b)

WASHING, ICING

Aquaculture prawn

Wild caught prawn

0-7

0-30

1-4h

1-4h

1 log reduction

(c)

ICING

Icing during transport (including

on board fishing vessel for wild

caught prawn) to processor

0-7 2-16h (cultured)

2-48h (wild)

2-3 log reduction (d)

WATER USE AT

PROCESSING

4-10 1-3h No effect (a) (b)

TEMPERATURE

Temperature during processing

before freezing

4-10 2-8h No effect (a) (b)

COOKING

Cooking at processing plant >90 0.5-1.0 min

(holding time at

>90ºC)

>6 log reduction (e) (f)

FREEZING

Freezing of cooked and raw

products, storage, and shipment

time

-12-20 15-60 d 2-6 log reduction (g) (h)

Source: (a) Industry data for time, temperature (personal communication M/S Sterling Seafoods, Mangalore,

India, 2002) (b) Kolvin and Roberts (1982) for multiplication; (c) Dinesh, 1991; (d) Karunasagar (personal

communication, Karunasagar, India, 2002); (e) Based on industry data on total plate count (Pers. Comm. M/S

Sterling Foods Mangalore, India) (f) In prawn homogenate D82.2=0.28 (Hinton and Grodner, 1985); (g)

INFOFISH (Pers. Comm) for shipment time, Reilly and Hackney (1985); Nascumento et al. (1998) for survival

in frozen prawn

Since contamination with V. cholerae is likely to be external, the site of greatest

microbiological concern for prawns is the carapace. From the foregoing, it is clear that the

site of microbiological concern receives a highly lethal heat treatment e.g. D82 = 0.28 min in

prawn homogenate (Hinton & Grodner, 1985). Thus, with at least 60 seconds at >90°C, the

lethality is greater than 6 log units.

Post-cooking processing involves rapid chilling (ice slurry) prior to freezing. On board

processing involves plate freezing while on-shore factories usually produce individually

quick frozen (IQF) prawns. The opportunity for post-cooking re-contamination (from water,

ice or handlers) of prawn is minimised by GHPs and SSOPs.

It is generally accepted that freezing reduces the concentration of contaminating vibrios, as

does frozen storage. According to industry sources in India (M/S Sterling Seafoods, personal

communication, 2002), the time interval between packing and the item reaching port-of-entry

is usually > 30 days, with INFOFISH data indicating a range of 15 to 56 days.

24

The foregoing traces a processing continuum in which, at various stages, there is progressive

inactivation of V. cholerae, particularly when product is held under refrigeration (iced or

frozen), of the order of 5–6 log units. Cooking leads to additional inactivation of the order of

6 log units. Further inactivation during freezing and frozen storage provides an explanation

for the lack of any documented involvement of internationally traded prawn in outbreaks of

cholera in prawn importing countries.

As part of a risk assessment on V. cholerae in warm-water prawns, FAO/WHO obtained port-

of-entry testing data from Japan, USA and Denmark. Of the more than 20,000 tests, over the

period 1995-2000, two samples (in 1995) tested positive for choleragenic V. cholerae

The ability of modern hygienic standards by prawn exporters was amply demonstrated during

the Peruvian cholera epidemic in 1991. DePaola et al. (1993) showed that, while choleragenic

V. cholerae O1 was present in all five samples of raw seafood collected from street vendors

in Lima and Callao, it could be isolated from only one out of 1,011 samples of seafood

destined for export.

2.7 Distribution and retail

Since the product is stored under frozen or refrigerated conditions, the retail market in

importing countries provides little opportunity for contamination or multiplication of

V. cholerae in prawns. This is supported by epidemiological data from countries such as

Japan and the United States of America, where prawn consumption is high (estimated annual

servings 8.58 and 12.5

8, respectively) and reported numbers of domestically acquired cholera

cases are absent or very low (Table 17). There are no reports of either outbreaks or sporadic

cases of cholera associated with imported prawn.

Table 17: Cases of cholera notified to WHO from major shrimp importing countries. (Source: Weekly Epidemiological Record)

Cholera Cases

Country 1995 1996 1997 1998 1999 2000

Japan 311 (295i) 1 39 (35i) 89 (55i) 60 (57i) 40 34 (32i)

USA 19 (19i) 32 4 (4i) 15 (15i) 6 (6i) 4 (1i)

Spain 6 (6i) 1 (1i) - - - 1 (1i)

France 5 (5i) 6 (6i) 3 (3i) 2 (2i) - -

Netherlands 9 (9i) 3 (3i) 2 (2i) 4 (4i) 2 (2i) -

UK 10 (10i) 13 (13i) 6 (6i) 18 (18i) - 33 (33i)

Canada 7 (7i) 2 (2i) - 2 (2i) - 5 (2i)

Hong Kong3 6(4i) 4(1i) 14 71(38i) 18(11i) 9 (3i)

Germany4 1 (1i) - 2i 5 (5i) 3 (3i) 2 (2i) 1 i: imported cases (WHO 2001)

2 1 case in Guam and 1 case in Saipan reported by the CDC

3From 1997 Hong Kong Special Administrative Region of China

4 Not in top ten importing countries but considered in the risk assessment due to the availability of relevant data

25

2.8 Consumption

As a generalisation, in importing countries, cold chain systems linking distribution, home and

food service prevent temperature abuse. A survey by Audits International (2000) indicated

that only 1.5% of home refrigerators operated warmer than 10°C, the minimum temperature

for growth of V. cholerae.

Where data are not available on consumption patterns, the mean serving size may be assumed

to be 275 g/meal, though, in reality, the edible portion will be <275 g after the carapace and

cephalothorax have been removed prior to consumption. This assumption was made on the

basis of an average serving of prawn consisting of 10 small prawns, described as weighing

between 25 and 30 g or five large prawns, described as weighing 50–65 g (Winkel, 1997).

In international trade, prawns are marketed frozen in both the raw and cooked forms. In the

cooked form, prawns are consumed without further heat treatment. Typically, raw prawns are

cooked before consumption, though, with the growing popularity of sushi and sashimi, a

proportion is eaten without further heat treatment; this proportion might be expected to be

higher in Japan than in the other countries.

3. Hazard Characterisation

V. cholerae O1 and O139 cause the illness known as cholera, which in its severe form,

cholera gravis, is an illness characterised by the passage of voluminous stools leading to

dehydration. If untreated, the resulting dehydration can lead to hypovolemic shock and the

death of the patient within 18 hours to several days of onset of symptoms, or sooner in

extreme cases (Bennish, 1994). The case-fatality rate in untreated cases may reach 30-50%.

However, treatment is straightforward and, if applied appropriately, the case-fatality rate is

less that 1% (WHO, 2004).

V. cholerae is sensitive to acid and therefore must successfully pass the acid barrier of the

stomach in order to cause infection. Choleragenic V. cholerae are known to have several

genetic factors related to virulence. In order to establish and multiply in the human small

intestine, the organism requires one or more adherence factors that enable them to attach to

the microvilli or intestinal epithelial cells (Kaper et al. 1995). The ctx operon is, however, the

primary factor associated with choleragenicity because it codes for cholera toxin (CT), which

is made up of an A and B subunit and is responsible for the symptoms of cholera. These

include the disruption of ion transport, with the subsequent loss of water and electrolytes,

leading to severe diarrhoea.

This toxin is secreted by the choleragenic V. cholerae O1 and O139 strains. The O1

serogroup can be classified into three main sub-groups: Ogawa, Inaba and Hikojima. Strains

may be subclassified into two biotypes: Classical and El Tor (Kaper et al. 1995). Genetic

studies have shown that the V. cholerae O139 choleragenic strain has evolved from an El Tor

biotype (Faruque et al. 2003).

3.1 Characteristics of the host

The host immune system is the critical defence mechanism against cholera. However,

infection with cholera can result in a range of responses, from severe and life threatening

diarrhoea to mild or non-clinical infections. In endemic areas, for example, only a minority

(20–40%) of infections with V. cholerae O1 El Tor results in any illness (Bart et al. 1970;

Shahid et al. 1984).

26

Prior immunological experience is an important factor and reports of much higher attack rates

in children compared with adults in cholera-endemic areas support this (Glass et al. 1982).

Another factor may be differences in gastric acidity. As gastric acid is an important defence

mechanism against cholera, low acid production can lead to increased susceptibility (Nalin et

al. 1978; Van Loon et al. 1990).

Recurrent infections of cholera are rare and volunteer studies have shown that clinical cholera

infection confers 90 to 100% protection against subsequent re-challenge with choleragenic

V. cholerae (Cash et al. 1974; Levine et al. 1979, 1981; Levine, 1980). In addition,

epidemiological studies in endemic areas have indicated that immunity follows an initial

natural cholera infection (Glass et al. 1982).

Pregnant women appear to experience a more severe form of the disease than non-pregnant

women. In addition, foetal loss is high, with one report indicating a foetal death rate of 50%

among women in their third trimester of pregnancy who developed severe dehydration from

cholera (Hirschhorn et al. 1969).

A number of demographic and socioeconomic factors, such as age, gender, nutritional status,

social status, economic status and travel abroad, all play a role in susceptibility to

choleragenic V. cholera.

Infection is known to be more severe in individuals suffering from malnutrition, with

Hypochlorhydria associated with malnutrition, B12 deficiency and gastritis predisposing to

the development of cholera. However, under nutrition does not seem to be associated with

increased risk (Richardson, 1994).

In cholera-endemic areas, children 2–15 years are considered most susceptible to cholera

when this group experiences initial infection (Glass et al. 1982). The symptoms of first

infections are severe, but rarely are people hospitalised a second time for the disease,

suggesting that immunity is long lasting and protective against severe illness. Breastfeeding

appears to be an important factor in reducing susceptibility to cholera among infants and

young children. One study indicated 70% reduction in the risk of severe cholera among

breast-fed children (Clemens et al. 1990). In cholera-endemic areas, women of childbearing

age (15–35) are commonly infected. In developed countries where hygienic standards are

high, all age groups are equally susceptible (Kaper et al. 1995). Most cases in countries

where high hygienic standards exist are imported cases, in that exposure to V. cholerae

occurred while travelling in another country.

Among host susceptibility factors, the association between cholera and blood group is

notable. Barua and Paguio (1977) and Chaudhuri and De (1977) noted that the incidence of

cholera in patients with blood group A was lower than that in the general population, while

incidence in those with blood type O was significantly higher. The likelihood of V. cholerae

infection progressing to the severe form, cholera gravis, appears to be related to the

individual’s ABO blood group (Levine et al. 1979). Thus, individuals with blood group O are

more likely to exhibit severe diarrhoea. In terms of genetic factors, there is a hypothesis that

those heterozygous for the cystic fibrosis allele are apparently less susceptible to severe cases

of cholera (Rodman & Zamudio, 1991).

3.2 Characteristics of the food matrix

While choleragenic V. cholerae O1 ingested with food is likely to be protected from gastric

acid, human volunteer studies have produced mixed results. In one study, human volunteers

ingested 106 V. cholerae O1 El Tor with 2 g of sodium bicarbonate (NaHCO3) in 300 mL

27

water or with a meal of fish, rice, milk and custard (Levine et al. 1981). Volunteers who

ingested V. cholerae with water alone did not become infected, but those who ingested the

organism in a meal had cholera of similar severity and attack rate to those who had buffered

gastric acidity with NaHCO3 (Levine et al. 1981). By contrast, experiments by Cash et al.

(1974) showed different results (see below).

Choleragenic V. cholerae appear to be relatively sensitive to both low pH and to dehydration.

The pH sensitivity of V. cholerae is illustrated by the epidemiological data of St Louis et al.

(1990), who observed that, in an epidemic in Guinea, West Africa, the cholera patients were

more likely to have eaten left-over peanut sauce (pH 6.0) but less likely to have eaten tomato

sauce (acid). This was further confirmed by laboratory studies in which V. cholerae

multiplied rapidly in peanut sauce but not in more acidic tomato sauce.

V. cholerae O1 are extremely sensitive to an acidic environment (Dalsgaard et al. 1997). In

gastric juice with pH <2.4, V. cholerae O1 were inactivated rapidly (Nalin et al. 1978; Levine

et al. 1984). Since V. cholerae O1 are transmitted via the oral route only, the organisms must

pass through the gastric acid environment of the stomach to colonise the intestine. In

normochlorhydric adult volunteers, doses of up to 1011

pathogenic V. cholerae O1 given

without buffer or food did not reliably cause illness, whereas doses of 104–10

8 organisms

given with 2 g of NaHCO3 resulted in diarrhoea in 90% of individuals (Cash et al. 1974). The

characteristics of illness in individuals with 106 organisms given with 2 g of NaHCO3 were

similar to that of cholera. In another volunteer study, doses of 105, 10

4 and 10

3 organisms

resulted in a 60% attack rate, although the diarrhoeal illness at the two lower doses was

milder and appeared to have longer incubation periods (Levine et al. 1981).

Because of the nature of most foods associated with the unintended consumption of

V. cholerae, pH and water activity are probably not relevant in modelling survival of

V. cholerae in raw seafood. However, these parameters may be relevant in modelling the

growth of V. cholerae in other foods as a result of cross-contamination.

3.3 Public health outcomes

When illness occurs, V. cholerae O1 and O139 cause mild to severe gastrointestinal illness

and may bring about patient dehydration leading to death. Common symptoms include

profuse watery diarrhoea, anorexia and abdominal discomfort. In cholera gravis, the rate of

diarrhoea may quickly reach 500–1000 mL/h, leading rapidly to tachycardia, hypotension,

and vascular collapse due to dehydration (Kaper et al. 1995). About 20% of those who are

infected develop acute, watery diarrhoea and 10 to 20% of these individuals go on to develop

severe watery diarrhoea with vomiting (WHO, 2004).

3.4 Number of cholera cases reported to WHO by prawn importing countries

Cholera is one of the diseases requiring notification to WHO according to the International

Health Regulation. It is worth noting that the United Kingdom (Adak et al. 2002) and the

United States of America (Mead et al. 1999) estimate that 50% of all cholera cases are

reported, which is high compared with the level of reporting of some other gastrointestinal

illnesses, such as non-typhoidal salmonellosis and campylobacteriosis, for which actual cases

are estimated to be 38 times more than reported cases (Mead et al. 1999).

In the available documentation, none of the cholera cases reported has been associated with

consumption of imported prawns. Except for a few, all cholera cases in the United States of

America and European countries were overseas-acquired. The United States of America has

28

an endemic focus of V. cholerae in Gulf Coast waters and has experienced sporadic cases and

small clusters of cholera related to the domestic consumption of contaminated seafood from

those waters (Blake et al. 1980; Blake et al. 1983). Japan has reported an increasing number

of apparent domestically-acquired cholera cases (IASR, 1998). The reason(s) for this increase

is unknown, cases typically being sporadic with no known aetiology.

In Australia, data from the National Enteric Pathogens Surveillance Scheme (NEPSS)

indicates a small number of reported annual illnesses from V. cholerae; over the period 2006-

2009 there were a total of 17 reports, of which 13 were overseas-acquired.

3.5 Dose-response relationship

Dose-response relationships can be developed from epidemiological investigations of

outbreaks and sporadic case series, human feeding trials or animal models of a particular

pathogen and related (surrogate) pathogens. In this instance, human feeding trial data were

available for V. cholerae and were used in the development of the dose-response curve.

There are numerous studies and references in the literature to the infectious dose of

choleragenic V. cholerae. The most commonly reported infectious dose is approximately 106

organisms or more (Levine et al. 1981; Tauxe et al. 1994; Health Canada, 2001; FDA, 2003).

While, as indicated above, there are numerous other factors that influence whether or not a

person becomes ill after ingestion of choleragenic V. cholerae, this estimate was used in both

the qualitative and semi-quantitative risk characterisations described later. A number of

human volunteer studies are available for choleragenic V. cholerae. Although these are

between 15 and 30 years old, they are the best data available in terms of providing an insight

into the dose response of the organism. These data are used as a basis to develop a dose-

response model, as described below.

Human volunteer data are available for the Classical and El Tor biotypes and Inaba and

Ogawa serogroups of V. cholerae O1. Cash et al. (1974) studied Classical Inaba and Ogawa

strains, while Levine et al. (1988) and Black et al. (1987) studied El Tor Inaba and Ogawa

strains. The results from these studies are shown in the dose-response curve presented in

Figure 2. As noted above, volunteer data were also available for V. cholerae O139.

Many choleragenic V. cholerae O1 and O139 infections result in the serious condition called

cholera gravis, which can be life threatening. There are no specific sequellae associated with

the severe form of illness other than the risk of death.

While illness due to choleragenic V. cholerae O1 and O139 is observed to occur in families,

it is thought that a common source of primary infection, rather than secondary transmission,

is the more likely mode of transmission (Glass & Black, 1992). While there is anecdotal

indication that direct person-to-person transmission may occur, it has never been

demonstrated by rigorous scientific study (Mintz et al. 1994).

The probability of death as the result of choleragenic V. cholerae O1 and O139 is dependent

on the public health infrastructure of the locality where the case of cholera is acquired. The

cornerstone in cholera therapy is rapid oral rehydration. Administration of antibiotics may

shorten the duration of diseases (Bennish, 1994). If adequate rehydration is not provided,

mortalities range between 20 and 50%. However, in most affected developing countries,

mortality rates are less than 5% where oral electrolyte solutions are available (Glass and

Black, 1992).

29

3.6 Dose-response model

In this assessment, a dose-response curve can be obtained by fitting the approximate Beta-

Poisson model to the data available from several volunteer studies (Cash et al. 1974; Levine

et al. 1981, 1988).

Pr(ill)=1−(1+ dose)−α β

Firstly, in the study by Cash et al. (1974), volunteers were exposed to a range of doses of the

Classical biotype of V. cholerae O1 in a food matrix (beef broth). The same organism was

given also to human volunteers together with an acid-neutralising solution. A dose-response

model was developed by FAO-WHO (2005) using both of these data sets, and resulted in a

dose- response curve with higher attack rates at lower doses in volunteers given the organism

with an acid-neutralising solution compared with a food matrix (Figure 2). The study of Cash

et al. (1974) was comprehensive as it examined a range of V. cholerae doses administered

both with a food matrix and with an acid-neutralising solution. However, as recent studies

have shown that the Classical biotype strains are rarely isolated from any part of the world

(Sack et al. 2003) these data were not considered to be the most appropriate for developing a

dose-response model relevant to current exposure to choleragenic V. cholerae.

The studies of Levine et al. (1981, 1988) focused on the El Tor biotype of choleragenic

V. cholerae and exposed volunteers to V. cholerae in a food matrix, an acid-neutralising

solution and water. In contrast to the results of Cash et al. (1974), described above, there is

evidence provided by Levine et al. (1981) that there is no significant food matrix effect, and

that dose-response curves obtained from human volunteer studies where V. cholerae doses

administered with acid-neutralising solutions adequately model the consumption of

V. cholerae with food. In their study, they found that for an El Tor V. cholerae given to

human volunteers at a dose of 106 organisms, a similar response was observed whether the

dose was administered with an acid-neutralising solution or with a standard meal of fish, rice,

custard and skim milk (Levine et al. 1981).

The conflicting evidence provided by Levine et al. (1981) compared with Cash et al. (1974)

adds to the uncertainty of dose-response curve for V. cholerae. Whether this reflects a

difference in the two biotypes or not is not known. However, it is acknowledged that the

effect of the food matrix on the dose response when consuming pathogenic vibrios is an

important area for future research and represents a critical data gap for this risk assessment.

All of these data and the resulting dose-response curves are included in Figure 2. As the study

of Levine et al. (1988) looked at a range of doses (106, 10

8, 10

10), these data were used for the

development of a dose-response curve for the El Tor biotype.

Figure 2 essentially shows the maximum likelihood fit of the Beta-Poisson model to the

available feeding trial data. A human volunteer study with V. cholerae O139 reported similar

infectious doses as described for the O1 serotype (Cohen et al. 1999).

30

Figure 2: Beta-poisson dose-response curves for different strains of V. cholerae

KEY: = Classical with food matrix (Cash et al. 1974); – – – = fit to Classical with food matrix; □ = El Tor

with antacid (Levine et al. 1988); – · – · – · = fit to El Tor with antacid; ▲= Classical Inaba with antacid (Cash

et al. 1974); ; - - - - = fit to Classical Inaba with antacid; ◊ = miscellaneous El Tor strains tested; ∆ = Classical

Ogawa (Cash et al. 1974); ○ = El Tor with bicarbonate (Levine et al. 1981); ◘ = El Tor with food (Levine et al.

1981); X = El Tor with water (Levine et al. 1981).

4. Summary in the Australian Context

Data compiled by the National Enteric Pathogens Surveillance Scheme (NEPSS)

indicates that cholera is almost unknown in Australia and of the cases which are

reported, almost all are overseas-acquired.

In testing of imported prawns, AQIS occasionally isolated V. cholerae from a 25 g

sample; no further testing is done to determine whether the isolate is toxigenic.

There have been no cases of cholera in Australia linked with consumption of prawns

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36

Vibrio parahaemolyticus


Vibrio parahaemolyticus is a marine micro-organism occurring in estuarine waters

throughout the world. The organism was first identified as a foodborne pathogen in Japan in

the 1950s (Fujino et al. 1953). By the late 1960s and early 1970s, V. parahaemolyticus was

recognised as a cause of diarrhoeal disease worldwide, although most common in Asia and

the United States. Vibrios concentrate in the gut of filter-feeding molluscan shellfish such as

oysters, clams and mussels where they multiply and cohere. Although thorough cooking

destroys these organisms, oysters are often eaten raw and, at least in the United States, are the

most common food associated with Vibrio infection (Hlady, 1997).

In tropical and temperate regions, disease-causing species of Vibrio occur naturally in marine,

coastal and estuarine (brackish) environments and Desmarchelier (2003) reports that, in

Australia, pathogenic vibrios can be isolated from freshwater reaches of estuaries. The

occurrence of these bacteria does not correlate with numbers of faecal coliforms and

depuration of shellfish may not reduce their numbers. There is a positive correlation between

water temperature and both the number of human pathogenic vibrios isolated and the number

of reported infections, a correlation particularly marked for V. parahaemolyticus and

V. vulnificus.

This hazard sheet relies heavily on information updated by the joint FAO-WHO work on

Vibrios in seafoods (FAO-WHO, 2011).

1.1 Human incidence

In Asia, V. parahaemolyticus is a common cause of foodborne disease. In general, the

outbreaks are small in scale, involving fewer than 10 cases, but occur frequently. Prior to

1994, the incidence of V. parahaemolyticus infections in Japan had been declining, however,

in 1994-95 there were 1,280 reports of infection due to the organism (Anon., 1999). During

this period, V. parahaemolyticus food poisonings outnumbered those of Salmonella. For both

years, the majority of the cases occurred in the summer, with the largest number appearing in

August. From 1996-1998, there were 496 outbreaks, 1,710 incidents and 24,373 cases of

V. parahaemolyticus reported. The number of V. parahaemolyticus food poisoning cases

doubled in 1998 as compared with 1997 and again exceeded the number of Salmonella cases

(Anon., 1999). As in 1994-1995, outbreaks were more prevalent in the summer with a peak in

August and with few outbreaks during winter months. Boiled crabs caused one large-scale

outbreak, involving 691 cases. The increased incidence in Japan during 1997-1998 has been

attributed to an increased incidence of serovar O3:K6.

During 1997 and 1998 there were more than 700 cases of illness due to V. parahaemolyticus

in the United States, the majority of which were associated with the consumption of raw

oysters. In two of the 1998 outbreaks a serotype of V. parahaemolyticus, O3:K6, reported

previously only in Asia, emerged as a principal cause of illness for the first time. Subsequent

studies on these strains have revealed their pandemic spread. It was suggested that warmer

than usual water temperatures were responsible for the outbreaks.

In Europe few data exist on the incidence of V. parahaemolyticus infections, one reason

being that such infections are not notifiable. However the current knowledge of the incidence

in Europe has been summarised in Opinion of the Scientific Committee on Veterinary

Measures relating to Public Health on Vibrio vulnificus and Vibrio parahaemolyticus in raw

37

and undercooked seafood issued by the European Commission (European Commission,

2001).

In Australia, the reported incidence is low, probably reflecting the consumption of seafood

which is, with the exception of oysters, usually eaten fully cooked. Gastroenteritis caused by

this organism is almost exclusively associated with seafood consumed raw or inadequately

cooked or contaminated after cooking. In the USA, illness is most commonly associated with

crabs, oysters, shrimp and lobster (Twedt, 1989; Oliver & Kaper, 2007). In Australia,

outbreaks have been associated with prawns and oysters (Kraa, 1995).

There have been no reports of its presence in Australian prawns except for one of 63 samples

tested in New Zealand (Lake et al. 2003); no information is provided on whether the isolate

was toxigenic.

The incidence of V. parahaemolyticus in prawns in various countries, some of which are due

to imports is presented in Table 18.

Table 18: Incidence of V. parahaemolyticus in prawns

Country (% positive, number of

samples)

Biotype information Reference

UK Retail cooked prawns

and shrimps (0/148)

None detected Greenwood et al. 1985

India Crustaceans (79.3%), Not reported Lall et al. 1979

India Fish and shrimps from

coastal waters (60%)

Not reported Qadri & Zuberi 1977

China Prawns (25%) Not reported Shih et al. 1996

Hong

Kong

Prawns (4/50, 8%) 2.5% KP+ Yam et al. 2000

Hong

Kong

Prawns 32/g Chan et al. 1989

Japan

(imports)

Raw prawns (26.3%,

21/80)

Tdh positive by PCR.

Isolates mostly O3:K6

Hara-Kudo et al. 2003

Mexico Prawns (27.6%) Not reported Vitela et al. 1993

Taiwan Raw prawns (25%,

10/40)

Not reported Wong et al. 1995

Taiwan

(imports)

Prawns (Thailand)

(75.8%, 47/62)

Isolates did not contain

tdh or trh gene

Wong et al. 1999

1.2 Foods implicated

V. parahaemolyticus occurs in a variety of fish and shellfish including clams, shrimp, lobster,

crayfish, scallops and crabs as well as oysters. Although oysters are the most common food

associated with Vibrio infection in some countries (Hlady, 1997), there have been reports of

V. parahaemolyticus infections associated with the other types of seafood:

Outbreaks of V. parahaemolyticus gastroenteritis aboard two Caribbean cruise ships

were reported in 1974 and 1975 (Lawrence et al. 1979). The outbreaks were most

likely caused by contamination of cooked seafood by seawater from the ships’

seawater fire systems.

38

In 1972, an estimated 50% of 1,200 persons who attended a shrimp feast in Louisiana

in the United States became ill with V. parahaemolyticus gastroenteritis (Barker &

Gangarosa, 1974) and samples of uncooked shrimp tested positive for the organism.

Three outbreaks occurred in Maryland in the United States in 1971 (Dadisman et al.

1972). Steamed crabs were implicated in two of the outbreaks after cross-

contamination with live crabs. The third outbreak was associated with crabmeat that

had become contaminated before and during canning.

A case-controlled study of sporadic Vibrio infections in two coastal areas of Louisiana

and Texas in the United States conducted from 1992-93, in which crayfish

consumption was reported by 50% (5/10) of the persons affected with

V. parahaemolyticus infection (Bean et al. 1998).

An outbreak in Louisiana in 1978 comprising 1133 cases was linked with raw shrimp

shipped in wooden boxes, which were boiled, returned to the same boxes and

transported unrefrigerated prior to consumption 7-8h later (Morbidity & Mortality

Reports, 1978; also cited by Oliver & Kaper, 2007).

More recently, sampling studies in the Adriatic Sea demonstrated the presence of

V. parahaemolyticus in fish, mussels and clams (Baffone et al. 2000) and in mussels

from the North-western coast of Spain. V. parahaemolyticus was isolated from 8% of

samples (European Commission, 2001).

There have been two large outbreaks of V. parahaemolyticus gastroenteritis in

Australia linked with consumption of prawns. In 1990 an outbreak affecting more

than 100 people, one of whom died, was linked to chilled, cooked prawns from

Indonesia. In 1992 there were two outbreaks affecting more than 50 people linked to

the same wholesale supplier of cooked prawns (Kraa, 1995).


A process model for exposure assessment involves the possibility of contamination and of

changes in population during harvest, processing, retail and at household level during

preparation for consumption (Figure 3).

Prevalence of V. parahaemolyticus is associated with the presence of particulates,

zooplankton and other chitin sources (Kaneko & Colwell, 1978; NACMCF, 1992;

Venkateswaran et al. 1990). Several studies have shown that Vibrio spp. are capable of

surviving and multiplying within certain protozoa such as Amoeba (Barker & Brown, 1994).

It has also been reported that V. parahaemolyticus ‘over-winters’ in the sediment and is

absent from the water column and oysters during the winter months (Joseph et al. 1983;

Kaysner et al. 1989; United States Department of Health and Human Services Food and Drug

Administration, 1995). Under extreme environmental conditions V. parahaemolyticus, may

enter a ‘viable but non-culturable’ (VBNC) phase in marine waters and could be missed by

traditional cultural methods (Bates et al. 2000; Colwell et al. 1985; Oliver, 1995; Xu et al.

1982).

Until relatively recently, there have been no studies on the existence of pathogenic strains of

V. parahaemolyticus. In the summer of 2001-02, Lewis et al. (2002) undertook a pilot study

of prevalence of total and pathogenic V. parahaemolyticus from leases in NSW, SA and

Tasmania (Table 5). The organism was isolated from 16/20 (80%) of oysters from NSW, 6/10

(60%) from Tasmania and 2/10 (20%) from SA. The study by Lewis et al. (2002), based on

39

only 40 samples of oysters from three states, was not regarded as definitive in the quantitative

sense and a longitudinal study over an annual cycle was recommended. However, the study

did isolate pathogenic strains, a finding of qualitative importance, especially for those areas

where water temperatures are high for several consecutive months.

Such a study was undertaken in the summer of 2006-7 when Madigan et al. (2007)

investigated South Australian oysters for presence of pathogenic vibrios. In 25 samples, each

of twelve oysters, V. parahaemolyticus was isolated from four, of which three were trh+ and

none was tdh+. Interestingly, while sucrose-negative vibrios (a category which contains

V. parahaemolyticus) were relatively high (103-10

4/g) during warmer months,

V. parahaemolyticus was isolated only after oyster samples were pre- enriched and molecular

techniques were employed. When samples were enumerated the researchers considered

pathogenic V. parahaemolyticus was present at below the limit of detection (<10/g) in oyster

meat. It should be noted that some sucrose-negative vibrios (e.g. V. harveyi) do not cause

human infections and, even among sucrose negative V. parahaemolyticus, only a very small

proportion are tdh+ and hence pathogenic. Therefore presence of a sucrose-negative Vibrio

count per se, should not be overstated in terms of presence of pathogenic strains.

More recently, in response to international activity regarding allowable concentrations of

V. parahaemolyticus in seafood, a brief survey was undertaken of oysters grown in New

South Wales, South Australia and Tasmania. V. parahaemolyticus was detected in 25/31

samples, generally at low concentrations in SA and Tasmanian oysters and ranging to

75 MPN/g in NSW oysters, where temperature and salinity were more favourable for the

organism. In the 25 samples positive for the organisms, the tdh gene was recovered from two

and trh from one sample, at low concentration (Madigan & May, 2010).

The three studies (above) indicate that, while V. parahaemolyticus is present in Australian

waters, the ratio of pathogenic strains appears low.

2.1 Harvest, post-harvest handling and transport

Marine prawns harvested by trawling are separated from the by-catch by manual sorting and

then iced on board. Ice is generally produced using potable water in coastal ice plants and

taken on board in insulated containers. It is likely that V. parahaemolyticus will be present at

low prevalence and low concentration after on-board processing.

In the case of cultured prawns, contamination with V. parahaemolyticus may occur during

harvest and handling before the prawns are washed and chilled. The implementation of GHPs

and HACCP along the chain should mean that this is low. Control points include dipping or

washing in water, icing and packing in plastic crates for transport by truck to the processing

plant.

2.2 Processing and cooking

Prawns intended for export are processed in facilities, including prawn trawlers, which meet

sanitary requirements for GHPs, GMPs and HACCP, where they are peeled manually or by

machine, then washed, graded, processed (e.g. heading, gutting) and, in some cases cooked,

before being packed for freezing.

Cooking is undertaken for several reasons, most important of which are customer

specifications or the prevention of melanosis (black spot formation), which can occur in the

head during chilled storage. In Australia, Winkel (1997) studied the effect of cooking on

40

black spot formation and organoleptic quality of Penaeus monodon. Winkel established that a

core temperature of 75°C was sufficient to cook the flesh, but that prevention of black spot

required a core temperature of 85°C. The time required to reach a 75°C core temperature was

related to the size of prawn: almost four minutes for ‘large’ (50–65 g) prawns and

1.5 minutes for ‘small’ (25–30 g) prawns.

As part of an Australian code of practice for farmed prawns, Sumner (1997) observed prawn

processing at six processing plants. Operators lowered each batch into ‘boiling’ water

(ca 98°C) in a proportion of around 5:1 (water:prawn), a procedure which lowered the water

temperature to around 92°C. The source of heat – usually a gas-fired ring – was then

maximised and the water quickly brought to ‘boiling’ (ca 98°C), at which time the operator

activated the timing device for the process. Since overcooking results in poor organoleptic

quality and weight loss, cooking time is important. Depending on size, prawns were cooked

for between 0.5 minute (‘small’) and 1.0 minute (‘large’), then immediately plunged into an

ice-water slurry to bring an end to cooking.

Post-cooking processing involves rapid chilling (ice slurry) prior to freezing. On board,

product is plate-frozen in the carton while on-shore factories usually produce individually

quick frozen (IQF) prawns. The opportunity for post-cooking re-contamination (from water,

ice or handlers) of prawn is minimised by GHPs and SSOPs.

It is generally accepted that freezing reduces the concentration of contaminating vibrios, as

does frozen storage. According to industry sources in India (M/S Sterling Seafoods, personal

communication, 2002), the time interval between packing and the item reaching port-of-entry

is usually > 30 days, with INFOFISH data indicating a range of 15 to 56 days.

2.3 Distribution and retail

Since the product is stored under frozen or refrigerated conditions, the retail market in

importing countries provides little opportunity for contamination or multiplication of

V. parahaemolyticus in prawns.

2.4 Consumption

In importing countries, cold chain systems linking distribution, home and food service

prevent temperature abuse. There is no information on prawn consumption in Australia or in

countries to which Australian product is exported. An assumption may be made that the mean

serving size is 275 g/meal, though, in reality, the edible portion will be <275 g after the

carapace and cephalothorax have been removed prior to consumption. This assumption was

made on the basis of an average serving of prawn consisting of 10 small prawns, described as

weighing between 25 and 30 g (average 27.5 g) or five large prawns, described as weighing

50–65 g (Winkel, 1997).

In international trade, prawns are marketed frozen in both the raw and cooked forms. In the

cooked form, prawns are consumed without further heat treatment. Typically, raw prawns are

cooked before consumption, though, with the growing popularity of sushi and sashimi, a

proportion is eaten without further heat treatment; this proportion might be expected to be

higher in Japan than in the other countries.

41

Figure 3: Production-consumption pathway for exposure assessment of V. parahaemolyticus in warm-water prawns

V. parahaemolyticus/g in ice

V. parahaemolyticus/ml in water

V. parahaemolyticus/ml

in water

Time and temperature

of frozen storage

CONSUMPTION Prawns thawed, prepared and eaten

HARVEST

Coastal areas

wild caught or from

aquaculture ponds

V. parahaemolyticus/g

POST HARVEST

HANDLING AND

TRANSPORT Prawns washed and iced


PROCESSING Prawns washed, peeled,

graded, packed and frozen


DISTRIBUTION AND

RETAIL Frozen prawns in international

transport, wholesale storage,

supermarkets and restaurants


No. of V. parahaemolyticus/g

ingested

COOKING Graded prawns cooked,

cooled, packed, frozen


Time and temperature

of frozen storage

42

2.5 Growth and survival characteristics

V. parahaemolyticus is a mildly halophilic, mesophilic micro-organism and its general

growth characteristics are shown in Table 19 (ICMSF, 1996). Warmer temperatures and

moderate salinity favour the survival and growth of V. parahaemolyticus (Covert &

Woodburne, 1972; Jackson, 1974; Nair et al. 1980; Zhu et al. 1992). A correlation exists

between V. parahaemolyticus infection and environmental temperatures with most of the

shellfish-borne illnesses caused by this organism occurring in the warmer months. This has

been observed in the United States, Asia and Europe (Daniels et al. 2000; Geneste et al.

2000).

Although outbreaks of foodborne disease associated with V. parahaemolyticus are less

commonly reported in Europe, there have also been a number of studies that indicate the

importance of temperature in the survival and growth of Vibrio. In a two year study

undertaken in Italy on seawater and molluscs from the Adriatic Sea it was found that Vibrio

strains were most prevalent during the summer months (Croci et al. 2001). In another study

conducted in Norwegian waters V. parahaemolyticus was only detected in July and August

(Gjerde & Bøe, 1981).

In France, hydrobiological monitoring carried out near nuclear power plants built on the

seashore, showed that the most spectacular effect was on the density of vibrios. The levels

were 100 times higher after the construction of the nuclear power plant than before, and

vibrios were found at a level of 105/L in its surrounds. Also, the annual decline in Vibrio

densities during the colder months of the year ‘overwinter’ no longer occurred (Gregoire et

al. 1993).

Table 19: Growth characteristics of Vibrio parahaemolyticus (ICMSF, 1996)

Optimum Range

Temperature (oC) 37 5-43

pH 7.8 – 8.6 4.8 –11

NaCl (%) 3 0.5 - 10

Water activity (aw) 0.981 0.940 – 0.996

Atmosphere Aerobic Aerobic - anaerobic

2.6 Growth rate

Growth of V. parahaemolyticus can be rapid, for example, doubling times of 27 minutes have

been reported in crabmeat at both 20 and 30°C (Liston, 1974). Growth rates in a range of

seafoods and tryptic soy broth with 2.5% salt (NaCl) have been recorded and summarised

(ICMSF, 1996). These data indicate that moderate populations of 102-10

3 organisms/g on

seafood can increase to >105 organisms/g in two to three hours at ambient temperatures of

between 20 and 35°C (ICMSF, 1996).

Miles et al. (1997) modelled the growth rate of V. parahaemolyticus based on studies of four

strains at different temperatures and water activity. For each combination of temperature and

water activity, bacterial growth was modelled using the Gompertz function, a sigmoid growth

curve with a growth rate (slope) monotonically increasing to a maximum before falling to

zero as the bacterial population reaches a steady state. The maximal rate of growth ( m) is the

most relevant summary of the fit because the growth rate approaches its maximum rapidly

43

and does not decline significantly until steady-state is reached. The model parameters

describe the range of temperature and water activity over which growth can occur. The

authors validated their model by comparing predicted growth with observed rates in eight

other studies of growth in broth systems obtained from the literature.

2.7 Death and inactivation

Although the ecology of V. parahaemolyticus has been studied (Joseph et al. 1983; Kaneko &

Colwell, 1978), little is known about the growth and survival of V. parahaemolyticus in

prawns. By contrast, post harvest growth of V. vulnificus in oysters has been studied

extensively (Cook, 1994; 1997) as have the effectiveness of various mitigation strategies for

reducing V. vulnificus (Cook & Ruple, 1992; Eyles & Davey, 1984; Motes & DePaola, 1996;

Richards, 1988; Son & Fleet, 1980). These include depuration, relaying, refrigerated storage

and mild heat treatment.


Dose-response relationships can be developed from epidemiological investigations of

outbreaks and sporadic case series, human feeding trials or animal models of

V. parahaemolyticus and related (surrogate) pathogens. In Japan, for example, human trials

showed an increase in the number of illnesses with increasing numbers of pathogenic

V. parahaemolyticus. Different dose-response models have been compared for the purpose of

extrapolating risk of illness estimated on the basis of human feeding trials at high levels of

exposure to the lower levels of exposure associated with consumption of raw oysters (Anon.

2005). The human feeding trials were conducted under conditions of concurrent antacid

administration.

3.1 Description of the pathogen, host and food matrix factors and how these influence the disease outcome.

Infection by V. parahaemolyticus is characterised by an acute gastroenteritis usually within 4-

30 hours of exposure. While most cases of V. parahaemolyticus infections are resolved

without medical intervention, on rare occasions infection can lead to septicaemia and death.

The virulence of V. parahaemolyticus appears to be largely attributable to thermostable direct

haemolysin (tdh +

) (Miyamoto, et al. 1969). Strains of V. parahaemolyticus expressing this

toxin lyse red blood cells on Wagatsuma agar and are also called Kanagawa positive (KP+);

tdh + and KP+ both indicate the presence of the toxin that is coded for by tdh+. The tdh

+

allele is seldom found in environmental isolates of V. parahaemolyticus, but is frequently

found in clinical isolates. Another genetic factor that may play a role in the virulence of

V. parahaemolyticus is trh+

(trh1 or trh2), an allele that codes for the TDH-related

haemolysin (Honda et al. 1988; Shirai et al. 1990; Kinushita et al. 1992).

3.2 Characteristics of the host

The immune system of the host responds to Vibrio spp infection to maintain health. The

immunocompromised are at special risk for both infection and for more severe sequelae. In

Japan cases of V. parahaemolyticus bacteraemia have been reported among patients who

were all immunosuppressed, especially with leukaemia and cirrhosis (Ng et al. 1999).

44

While there are no known measures of physiological status relating to susceptibility to

V. parahaemolyticus illness, analysis of epidemiological data indicate that pre-existing

illnesses may predispose individuals with gastrointestinal illness to proceed to septicaemia

(Anon., 2005).

In two epidemiological studies (Hlady, 1997; Klontz, 1990), V. parahaemolyticus accounted

for 77/339 reported Vibrio infections, of which 68 reported gastroenteritis and nine had

septicaemia; 29 persons were hospitalised for gastroenteritis with no deaths reported, while

eight were hospitalised for septicaemia, of whom four died. Patients with septicaemia had

underlying illness including, but not limited to, cancer, liver disease, alcoholism and Diabetes

mellitus (Hlady, 1997; Klontz, 1990).

Hlady and Klontz (1996) reported that, of patients with infections, 25% had pre-existing liver

disease or alcoholism. These included 75% of the septicaemia patients and 4% of the

gastroenteritis patients. Of the remaining septicaemia patients, nine reported having a history

of at least one of the following: malignancy, renal disease, peptic ulcer disease,

gastrointestinal surgery, diabetes, antacid medication and pernicious anaemia. Among the

gastroenteritis patients, 74% had none of the above pre-existing medical conditions or had

insufficient information to classify.

There are no known human genetic factors that appear to be related to the susceptibility of

individuals to V. parahaemolyticus illness.

3.3 Characteristics of the food matrix

Vibrio spp. appear to be relatively sensitive to both low pH and dehydration. Because of the

nature of most foods associated with the unintended consumption of Vibrio spp., pH and

water activity are probably not relevant in modelling survival of Vibrio spp. in raw seafood.

However these parameters may be relevant in modelling the growth of Vibrio spp. in other

foods as the result of cross contamination.

3.4 Public health outcomes

Gastroenteritis due to V. parahaemolyticus infection is usually a self-limiting illness of

moderate severity and short duration (Barker, 1974; Barker & Gangarosa, 1974; Levine et al.

1993). However, severe cases requiring hospitalisation have been reported. Symptoms

include explosive watery diarrhoea, nausea, vomiting, abdominal cramps and less frequently,

headache, fever and chills. On rare occasions, septicaemia, an illness characterised by fever

or hypotension and the isolation of the micro-organism from the blood, can occur. In these

cases, subsequent symptoms can include swollen, painful extremities with haemorrhagic

bullae (Hlady, 1997; Klontz, 1990). Duration of illness can range from two hours to 10 days

(Barker & Gangarosa, 1974).

An outbreak is defined as the occurrence of two or more cases of a similar illness resulting

from the ingestion of a common food. The incubation period ranges from 12-96 hours with a

median of approximately 15-24 hours. Although V. parahaemolyticus outbreaks are less

frequent in occurrence, sporadic cases are not infrequent.

According to statistics maintained by the National Enteric Pathogens Surveillance Scheme

(NEPPS) there are occasional reports of illness caused by V. parahaemolyticus. Over the

four-year period, 2006-2009, there were 34 reports of which 15 were acquired overseas.

45

3.5 Dose-response relationship

Human volunteer studies are available to estimate the probability of illness given exposure.

Sanyal and Sen (1974), Takikawa (1958) and Aiso & Fujiwara (1963) have conducted dose-

response investigations. In the United States, approximately 5% of culture-confirmed cases of

V. parahaemolyticus progress to septicaemia (Angulo & Evans, 1999). No reports were

identified describing secondary or tertiary transmissions of illnesses caused by

V. parahaemolyticus. Based on United States statistics, around twenty percent of patients

who are septicaemic with V. parahaemolyticus die (Angulo & Evans, 1999).

3.6 Dose-response model

Figure 4, taken from the US risk assessment on V. parahaemolyticus (Anon., 2005) shows the

maximum likelihood fit of the Beta-Poisson to the available feeding trial data. Due to the

small number of subjects exposed during these studies there is considerable uncertainty about

the best estimate of the dose-response.

Figure 4: Beta-Poisson dose-response curve for Vibrio parahaemolyticus


Not surprisingly, given the high temperature of Australian waters, V. parahaemolyticus is

a natural component of the microbiota.

Recently, pathogenic strains have been isolated from oysters.

Illness caused by V. parahaemolyticus is rare; over the four-year period 2006-09, there

were 34 reports of illness of which 15 were overseas-acquired.

This reflects the low concentration of the pathogen.

46

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51

Salmonella


Historically, prawns in international trade have been subjected to stringent import

regulations. In 1974 the United States Food and Drug Administration began the procedure of

blocklisting, described as ‘an effective action used against severe or chronic violations or

violators’. The practice was aimed at Asian prawn imports, which were tested for presence of

filth, decomposition and Salmonella, detection of which resulted in automatic detention of the

shipment and the placement of the supplier on an enhanced testing regime. The

contamination profile of prawns imported to the USA was determined by Gecan et al. (1994)

in which, inter alia, Salmonella was detected in 8.1% of samples. The European Union

similarly imposed bans on seafood imports including, in 1997, one on imports of prawns

from Bangladesh because of perceived public health risk.

Over recent decades there has been a shift in the type of prawn in international trade, from

exclusively marine in 1970s to largely warm-water, farmed prawns, from tropical countries.

Prawn farming involves exposure during growing and harvesting to animal and human waste,

which might be expected to introduce enteric and other pathogenic bacteria (Salmonella,

Escherichia coli, Campylobacter, Yersinia and Shigella).

Perhaps surprisingly, given the caution of major importing countries and blocs, there have

been few documented outbreaks of food poisoning from prawns in international trade

(Table 20). In the shigelloses outbreaks cited below, imported Asian prawns were

incriminated in the Dutch incident and the importing country was not identified in the UK

incident. The shigelloses indicate post-process contamination, possibly involving a food

handler in the carrier state, or the use of contaminated water.

Table 20: Documented outbreaks of illness from cooked prawns with enteric pathogens

Date Country Organism Impact Reference

1983-4 Holland Shigella flexneri 14 dead van Spreekens (1985)

1992 UK Shigella sonnei 119 ill Anon. (1992)

In 2010 an FAO working group gathered information on prawn-associated salmonellosis

from major importers (Anon. 2010). Unfortunately data were aggregated so that prawns were

subsumed with larger categories. However, as can be seen from Table 21, it is unlikely that

there is a strong linkage between prawns and salmonellosis.

Table 21: Seafood-associated salmonellosis in the EU and USA

Date Country Food Vehicle # Salmonellosis/

# Outbreaks

1998-2002 USA Crustaceans, shellfish,

molluscs and products

2/75

2007 EU Shellfish 2/151

52


2.1 Occurrence in the aquatic environment and in product

In Australia, prawns are consumed from several sources:

Estuarine prawns cooked on board the vessel

Aquaculture prawns, raw and cooked

Marine prawns, raw and cooked on board the vessel

Imported prawns, raw and cooked from tropical, mainly Asian, countries.

There has been very little published work on the microbiology of prawns caught and

processed in Australia (Norhana et al. 2010). Chinivasagam et al. (1997) reviewed the

process hygiene of prawns caught off Brisbane and cooked on board. In several cases post-

process contamination was established in the form of coliforms (some of which were faecal

coliforms) and S. aureus. In some cases Total Viable Counts approximated or exceeded

1 million/g indicating poor chilling aboard the vessel. Cooking and chilling aboard small

vessels is a difficult task, which may be exacerbated by poor water quality, especially in

estuaries.

Salmonella enters seafoods from the aquatic systems in two different patterns according to

the temperature characteristics of the area. In temperate waters, such as the United States and

the United Kingdom, prevalence of Salmonella on prawns was 7% and 8%, respectively

(Brands et al. 2005; Martinez-Urtaza et al. 2004; Wilson & Moore, 1996).

By contrast, in tropical areas, Salmonella incidence in seafood can reach up to 20%, as it has

been reported for areas of Asia and Africa (Hatha & Lakshmanaperumalsamy, 1997; Heinitz

et al. 2000). In Vietnam, an incidence of 18% of positive samples for Salmonella has been

reported for shellfish product (Van et al. 2007), while in India, presence of Salmonella was

found in 24.3% of different seafood products investigated (Rakesh Kumar et al. 2008). In

Table 22 are presented prevalence of Salmonella in environments and product in Asian

countries.

Despite that a significant proportion of prawns are caught in warm, northern waters of

Australia, they are cooked and frozen on board the vessel and together with aquaculture

prawns cooked in processing plants, they are most unlikely to be contaminated with

Salmonella.

Table 22: Salmonella in environment and products in Asian countries

Country

(n)

Sample Positive

(%)

Serovars Reference

Asia Prawns 1.6 Weltevreden, Paratyphi B,

Abaetetuba

Koonse et al. 2005

(1234) Pond water 3.5

Source water 5.0

Vietnam

(50)

Shellfish 18.0 - Van et al. 2007

India

(443)

Prawns 29 Weltevreden, Rissen,

Typhimurium

Kumar et al. 2008

53

In temperate and tropical regions presence of Salmonella in the environment is linked with

rainfall events, particularly after the first heavy rains associated with monsoonal events

(Baudart et al. 2000; Brands et al. 2005; Hatha & Lakshmanaperumalsamy, 1997; Martinez-

Urtaza et al. & Field, 1991; Venkateswaran et al. 1989). Water temperature has

been linked with survival of Salmonella in the environment, with cold waters reducing

survival and warm waters, together with high levels of organic matter, increasing survival.

In Table 23 is presented data for Salmonella prevalence in prawns imported to the USA over

a 10-year period (Gecan et al. 1994; Heinitz et al. 2000).

Table 23: Prevalence of Salmonella in prawns imported to USA

Country Product Prevalence

(%)

Reference

USA (1989-90) Raw prawns 17/211 (8.1) Gecan et al. (1994)

USA (1990-98) Raw crustaceans (imported) 365/3946 (8.5) Heinitz et al. (2000)

USA (1990-98) Raw crustaceans (domestic) 5/129 (3.9) Heinitz et al. (2000)

Asai et al. (2008) surveyed prevalence of Salmonella in seafoods imported to Japan. Of 212

samples, five (2.4%) were positive by PCR and 2/212 (0.9%) also yielded positive cultures,

both S. Weltevreden.

Serovar matching is sometimes used to imply linkage between a specific food product and

human illness. In 1981 Sumner noted that, in the UK and Australia, while S. Weltevreden

was the serovar most commonly isolated from imported prawns, it was rarely associated with

salmonellosis in these countries. However, this serovar is prevalent in Asian environments. In

Thailand, Bangtrakulnonth et al. (2004) determined its frequency in salmonelloses and in a

range of foods: frozen chicken (19.9%), frozen seafood (26.3%), frozen duck (12.0%), water

(14.5%). It is also a commonly-isolated serovar in raw seafood products from other Asian

countries, having been isolated from products in India (Shabarinath et al. 2007; Rakesh

Kumar et al. 2008) and in aquaculture prawns from other Asian countries (Reilly & Twiddy,

1992; Koonse et al. 2005).

Over the period 2006-09, S. Weltevreden accounted for around 1% of salmonelloses in

Australia, with a significant proportion being acquired overseas, particularly in visitors to

Bali (NEPSS data).

2.2 Growth and survival

Salmonella grows over a wide range of temperature, pH and water activity. It is a mesophile

with a minimum growth temperature (7°C) and has little salt tolerance (Table 24).

Table 24: Growth conditions for Salmonella (after ICMSF, 1996)

Conditions Minimum Optimum Maximum

Temperature (°C) 7 35-43 46

pH 3.8 7-7.5 9.5

aw 0.94 0.99 >0.99

54


Salmonella is a Gram-negative, facultative anaerobe. There are two species: S. enterica and

S. bongori, with strains that cause human illness included mainly in the subspecies S. enterica

subsp. enterica.

Salmonella are excreted in the faeces of animals and humans and is a component of the

natural aquatic microbiota in aquatic environments in tropical regions (Reilly & Twiddy,

1992). The pathogen is transmitted to humans via water or food contaminated with faeces, or

from infected food-handlers.

Many Salmonella serovars are motile and contain flagellar (‘H’) and somatic (‘O’) antigens.

Approximately 2,500 serovars have been described of which, globally, S. Enteritidis and

S. Typhimurium are the main serovars involved in human infection (Greig & Ravel, 2009). In

the Asian region, S. Weltrevreden is a common cause of salmonellosis (Galanis et al. 2006),

as is S. Typhi in Africa and South-East Asia.

There are two clinical manifestations of Salmonella:

Salmonella Typhi/Paratyphi causing enteric fever, with an incubation period ranging

from 7-28 days. Symptoms include malaise, headache, fever, cough, nausea,

vomiting, constipation, abdominal pain, chills, rose spots, bloody stools.

Non-typhoid Salmonella, causing gastroenteritis following 8-72 hours incubation.

Symptoms include abdominal pain, diarrhoea, chills, fever, nausea, vomiting and

malaise. The disease is generally self-limiting and resolves in one to three days.

Invasion of the gastrointestinal tract followed by bacteraemia may occur. S. Dublin

has a 15% mortality rate when septicaemic in the elderly, and S. Enteritidis has an

approximately 3.6% mortality rate in hospital/nursing home outbreaks, with the

elderly being particularly affected.

Reactive arthritis and Reiter's syndrome have also been reported to occur, generally after

three weeks. Reactive arthritis may occur with a frequency of about 2% of culture-proven

cases. Septic arthritis, subsequent or coincident with septicaemia, also occurs and can be

difficult to treat.

3.1 Pathogenicity and host factors

All age groups are susceptible, but symptoms are most severe in the elderly, infants and the

infirm. AIDS patients suffer salmonellosis frequently (estimated 20-fold more than the

general population) and suffer from recurrent episodes. Individuals with underlying disease

such as sickle-cell anaemia, liver and gall bladder disease, and immune deficiency are more

prone to septicaemia. Hypochlorhydria and achlorhydria increases susceptibility to infection

and the severity of disease.

The organism has several pathogenicity islands - Salmonella pathogenicity islands (SPI). At

present 12 different SPI have been described which contain genes influencing attachment,

invasiveness, production of toxins and survival/growth in the host (Hensel, 2004). Other

factors that affect the ability of the pathogen to cause disease include the presence of

cytotoxins and diarrhoeagenic enterotoxins. The enterotoxin is released into the lumen of the

intestine and results in the loss of intestinal fluids (D’Aoust, 1991).

55

3.2 Food matrix

While gastric acidity is an important defence, Salmonella can survive the gastric barrier in

foods of high fat content or in foods with high buffering capacity e.g. chocolates, cheese.

3.3 Dose-response

There have been a number of human feeding trials performed using six different serotypes

where, as a generalisation, there were usually no illnesses at doses less than 106. By contrast,

outbreak investigations have shown that dramatically fewer cells can cause infection

(Table 25).

Table 25: Salmonelloses produced by serovars at low dosage (after D’Aoust, 1991)

Vehicle Serovar Infectious dose

Chocolate S. Eastbourne 100

Chocolate S. Napoli 10-100

Chocolate S. Typhimurium <10

Cheese S. Heidelberg 100

Cheese S. Typhimurium 1-10

Hamburger S. Newport 10-100

It should be emphasized that prawns are not a high-fat food.


For more than three decades countries importing prawns from tropical countries have

searched, and occasionally found, Salmonella in uncooked prawns.

By contrast, globally, there have been few outbreaks of salmonellosis associated with

prawns (raw and cooked), despite the enormous volume of product in international trade.

There have been no reported salmonelloses in Australia from consumption of prawns.

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Van, T., Moutafis, G., Istivan, T., Tran, L. and Coloe P. 2007. Detection of Salmonella spp in

retail raw food samples from Vietnam and characterisation of their antibiotic resistance. Appl.

Environ. Microbiol. 73:6885–6890.

Venkateswaran, K., Takai, T., Navarro, I., Nakano, H., Hashimoto, H. and Siebeling, R.

1989. Ecology of Vibrio cholerae non–O1 and Salmonella spp. and role of zooplankton in

their seasonal distribution in Fukuyama coastal waters, Japan. Appl. Environ. Microbiol.

55:1591–1598.

Wilson, I. and Moore, J. 1996. Presence of Salmonella spp. and Campylobacter spp. in

shellfish. Epidemiol. Infect. 116:147–153.

58

Hepatitis A (HAV)


Hepatitis A is an enteric virus which multiplies in the gut of the host, is excreted in the faeces

and contaminates foods or surfaces, from where they are ingested either directly (from food)

or indirectly, when the hands pick up the virus from the surface. Thus enteric viruses are

transmitted via the faecal-oral route.

In Australia enteric viruses have been implicated in a large number of outbreaks, mainly

caused by Norovirus (NoV), but also by HAV (Table 26).

Table 26: Selected incidents of foodborne disease in Australia caused by enteroviruses

Year Vehicle Causative

Organism

Cases

(deaths)

Reference

1978 Oysters Norovirus >2,000 Murphy et al. (1979)

1989 Oysters Norovirus 1,200 Kraa (1990a, b)

1991 Orange juice Norovirus >4,000 Lester et al. (1991)

1996 Oysters Norovirus 93 Stafford et al. (1997)

1997 Oysters Hepatitis A 467 (1) Conaty et al. (2000)

From Table 26 it can be seen that enteric viruses have been involved mainly with shellfish

consumption, shellfish being able to concentrate virus particles from the watercourse because

of their filter-feeding habit. The orange juice outbreak was traced to contamination of the

potable water source to the factory.

In a review of viral outbreaks caused by consumption of fresh produce, Seymour and

Appleton (2001) state that NoV has been implicated in outbreaks from washed salads, frozen

raspberries, coleslaw, green salads, fresh cut fruits and potato salad and HAV in outbreaks

from iceberg lettuce, strawberries, diced tomatoes and salads.

In 2009 in Victoria there were two outbreaks of Hepatitis A from consumption of semi-dried

tomatoes, probably imported from Turkey, where Hepatitis A is endemic in certain rural

regions (Anon. 2009).

In 1997 a cluster of Hepatitis A infections were linked with a Sydney restaurant and

epidemiological investigation suggested that prawns imported from Burma were the likely

cause (Anon. 1997). It is not stated whether prawns were imported cooked, or whether they

were cooked and served in the restaurant. No further investigation was undertaken and no

conclusion could be reached on whether the contamination occurred during processing in

Burma or handling at the restaurant.


Viral hazards associated with consumption of seafood were the topic of a number of reviews

(Mosley, 1967; Goldfield, 1976; Gerba & Goyal, 1978; Richards, 1985; CDC, 1990; DeLeon

& Gerba, 1990; Sobsey et al. 1991; Fleet et al. 2000; Lees, 2000), the latter two reviewing

viral contamination of Australian oysters in the context of the Wallis Lake outbreak of 1997.

59

In summary, the main conclusions of these reviews were that:

Viruses causing disease in fish are not pathogenic to humans.

Food contaminated with human waste containing viruses that are infective via the

faecal-oral route, is a cause of foodborne disease.

Seafood can be contaminated with enteric viruses through exposure to raw or treated

sewage and during processing and preparation by contaminated water supplies and

infected food handlers.

Finfish and crustaceans are not usually associated with the spread of viral foodborne

disease unless contaminated by food handlers.

Consumption of both raw and cooked molluscan bivalves (shellfish) is a well-

documented cause of viral foodborne disease.

Virus particles can remain detectable for several months under certain conditions in

seawater and in food.

Shellfish depuration techniques do not totally eliminate viral particles.

Infectious doses are presumed to be low e.g. 10-100 virus particles.

Human enteric viruses do not replicate in seafood products so that time and temperature

of storage/handling are not risk factors.

Viruses are resistant to moderate heat and pH conditions.


Hepatitis A is classified within the Hepatovirus genus of the Picornaviridae family. HAV has

a single molecule of RNA surrounded by a small (27 nm diameter), non-enveloped, protein

capsid.

Hepatitis A is usually a mild illness characterised by sudden onset of fever, malaise, nausea,

anorexia and abdominal discomfort, followed by jaundice, perhaps up to four weeks after

exposure. The infectious dose is unknown but presumably is similar to other RNA enteric

viruses (10-100 virus particles). HAV is excreted in faeces of infected people and can infect

susceptible individuals when they consume contaminated water or foods. Water, shellfish and

salads are the most frequent sources. Contamination of foods by infected workers in food

processing plants and restaurants is common. The virus has not been isolated from any food

directly associated with an outbreak. Because of the long incubation period, the suspected

food is often no longer available for analysis (Sobsey et al. 1991; FDA, 1999). Shellfish have

been associated worldwide with a large number of hepatitis outbreaks (Tang et al. 1991; Xu

et al. 1992; Leoni et al. 1998).

3.1 Illness caused

The incubation period for Hepatitis A, which varies from two to six weeks (mean four weeks)

is dependent upon the number of infectious particles consumed. Infection with very few

particles results in longer incubation periods. The period of communicability extends from

early in the incubation period to about a week after the development of jaundice. The greatest

danger of spreading the disease to others occurs during the middle of the incubation period,

well before the first presentation of symptoms. Many infections with HAV do not result in

clinical disease, especially in children. When disease does occur, it is usually mild and

recovery is complete in one to two weeks. Occasionally, the symptoms are severe and

60

convalescence can take several months. Patients suffer from feeling chronically tired during

convalescence and their inability to work can cause financial loss. Less than 0.4% of reported

cases in the US are fatal, usually occurring in the elderly (Sobsey et al. 1991; FDA, 1999).

3.2 Unique host susceptibility factors

All people who ingest the virus and are immunologically unprotected are susceptible to

infection (Sobsey et al. 1991; FDA, 1999). Hepatitis A infection in children is normally

subclinical, while in adults overt hepatitis develops in the majority of individuals (Hollinger

& Ticehurst, 1990). Infection results in long-term immunity as older individuals are more

likely to have HAV antibodies than younger individuals. In one study of 245 blood donors,

57% of those aged 30-49 years were antibody positive, compared with only 30% of those

aged 18-29 years. Immunity appears to be protective as repeat attacks are rare (Boyd & Marr,

1980). Other host factors affecting the severity of hepatitis infection are poorly characterised.

Immune impairment is less significant than for other foodborne pathogens. Existing liver

damage (e.g. cirrhosis) may be significant (Cliver, 1989).


The NSW report of this enteric virus in prawns (Anon. 1997) is the only one in the

literature, as reviewed by Todd and co-workers at Michigan State University in a series

of publications (so far numbering 11) under the general heading ‘Outbreaks where food

workers have been implicated in the spread of foodborne disease’.

Given its unique quality, the lack of confirmation that prawns were the infecting agent in

the NSW outbreak, and of any other data it is not possible to estimate the risk of this

hazard:product pairing. Note this in contrast to the Hepatitis A outbreak in oysters from

Wallis Lakes in NSW, where there were sufficient data for Sumner and Ross (2002) to

produce a risk rating using Risk Ranger.

References

Anonymous. 1997. Hepatitis A outbreak in New South Wales. Communicable Diseases

Intelligence 21(13), 17.

Anonymous. 2009. Semi-dried tomatoes. Victorian government health information.

Boyd, R. and Marr, J. 1980. Basic medical microbiology. Pub: Little & Brown, Boston, USA.

CDC. 1990. Viral agents of gastroenteritis: public health importance and outbreak

management. Morbidity and Mortality Weekly Report, 39(RR-5):1-24.

Cliver, D. O. 1989. Foodborne viruses, p. 437-446. In M. P. Doyle (ed.), Foodborne Bacterial

Pathogens. Marcel Deker, Inc., New York.

Conaty, S., Bird, P., Bell, G., Kraa, E., Grohmann, G. and McAnulty, J. 2000. Hepatitis A in

New South Wales, Australia from consumption of oysters: the first reported outbreak.

Epidemiology and Infection. 124(1):121-130.

DeLeon, R., and Gerba, C.P. 1990. Viral Disease Transmission by Seafood. p. 639-662. In J.

O. Nraigu and M. S. Simmons (Eds.), Food Contamination from Environmental Sources.

John Wiley and Sons, Inc. New York.

FDA. 1999. Bad Bug Book (Foodborne Pathogenic Microorganisms and Natural Toxins).

61

URL http://vm.cfsan.fda.gov/~mow/intro.html

Fleet, G.H., Heiskanen, P., Reid, I., and Buckle, K.A. 2000. Foodborne viral illness – status

in Australia. International Journal of Food Microbiology, 59:127-136.

Gerba, C. P., and Goyal, S.M.. 1978. Detection and occurrence of enteric viruses in shellfish:

A review. Journal of Food Protection, 41:743-754.

Goldfield, M. 1976. Epidemiological Indicators for Transmission of Viruses by Water. p. 70-

85. In G. Berg, H. L. Bodily, E. H. Lennette, J. L. Melnick, and T. G. Metcalf (Eds.), Viruses

in Water. American Public Health Association, Washington, D.C.

Hollinger, F. B., and Ticehurst, J. 1990. Hepatitis A Virus, p. 631-667. In B. N. Fields and D.

M. Knipe (Eds.), Virology, Second ed, vol. 1. Raven Press, New York.

Kraa, E. 1990a. Oyster related food poisoning. NSW Public Health Bulletin:1(6):11.

Kraa, E. 1990b. Food poisoning outbreak, Sydney. Communicable Disease Intelligence:

14:7-9.

Lees, D. 2000. Viruses and bivalve shellfish. International Journal of Food Microbiology.

59:81-116.

Leoni, E., Bevini, C., Esposti, S.D. and Graziano, A. 1998. An outbreak of intrafamiliar

hepatitis A associated with clam consumption: Epidemic transmission to a school

community. European Journal of Epidemiology, 14(2):187-192.

Lester, J., Stewart, T., Carnie, J., Ng, S. and Taylor, R. 1991. Air travel-associated

gastroenteritis outbreak, August 1991. Communicable Disease Intelligence: 15:292-293.

Mosley, J. W. 1967. Transmission of Viral Disease by Drinking Water. In G. Berg (Ed.),

Transmission of Viruses by the Water Route. Interscience, New York

Murphy, A.M., Grohmann, G.S., Christopher, P.J., Lopez, W.A. and Davey, G.R. 1979. An

Australia-wide outbreak of gastroenteritis from oysters caused by Norwalk virus. Medical

Journal of Australia. 2:329-333.

Richards, G. P. 1985. Outbreaks of shellfish-associated enteric viruses illness in the United

States: requisite for development of viral guidelines. Journal of Food Protection, 48:815-823.

Seymour, I. And Appleton, H. 2001. Foodborne viruses and fresh produce. Journal of

Applied Microbiology. 91:759-773.

Sobsey, M., Cole, M., and Jaykus, L.A. 1991. Human Enteric Pathogenic Viruses. In M. D.

Pierson and C. R. Hackney (Eds.), Comprehensive Literature Review of Indicators in

Shellfish and their Growing Waters. Pierson Associates, Inc.

Stafford, R., Strain, D., Heymer, M., Smith, C., Trent, M. and Beard, J. 1997. An outbreak of

Norwalk virus gastroenteritis following consumption of oysters. Communicable Disease

Intelligence, 21:317-320.



Tang, Y. W., Wang, J.X., Xu, Z.Y., Guo, Y.F., Qian, W.H. and Xu. J.X. 1991. A

serologically confirmed, case-control study, of a large outbreak of hepatitis A in China,

associated with consumption of clams. Epidemiology and Infection, 107(3):651-7.

Xu, Z. Y., Li, Z.H. Wang, J.X. Xiao, Z.P. and Dong. D.X. 1992. Ecology and prevention of a

shellfish-associated hepatitis A epidemic in Shanghai, China. Vaccine, 10(Suppl 1):S67-68.


62

Chloramphenicol


In 2001 the European Union instituted a ban on seafood, mainly shrimp, containing the

broad-spectrum antibiotic, chloramphenical (CAP). Some countries destroyed batches of

shrimp containing CAP. The legislative framework for the ban, Council Regulation EEC No.

2377/90, was implemented to establish maximum residue limits (MRLs) of veterinary

medicinal products in foodstuffs of animal origin.

Chloramphenicol is active against a range of Gram-positive and negative bacteria and is

prescribed for topical application, especially in eye drops as treatment for bacterial

conjunctivitis (Lancaster et al. 1998).

A side-effect of CAP application treatment is aplastic anaemia, an effect rare and generally

fatal, though usually occurring weeks or months after treatment has stopped. Treatment is

also associated with bone marrow suppression.

In 2001, EU authorities imposed a ‘zero tolerance’ criterion for presence of chloramphenicol

which, with the capacity of modern analytical equipment yielded positives in the range µg/kg

(parts/million) to µg/t (parts/trillion). In the absence of information on a maximum allowable

level (from the toxicological viewpoints) EU authorities adopted the precautionary principle.

The assertion was that CAP was being used on prawns as an illicit veterinary chemical. This

assertion has been challenged by Hanekamp et al. (2003) on the grounds that CAP is:

A natural chemical, produced by Streptomyces spp, a ubiquitous soil bacterium.

A commonly-used antibiotic, particularly in Asian countries, where it is widely

available for over-the-counter purchase.

Its occurrence in aquaculture shrimp from Asian countries may therefore be from natural

and/or community sources.


As part of an EU Market Access Program, the South Australian Research and Development

Institute (SARDI) undertook residue testing of prawns in conjunction with the Australian

Prawn Farmers Association (APFA). Homan and Padula (2008) found that all samples of

prawns from six prawn farms had chloramphenicol levels below the laboratory limit of

detection (0.19µg/kg).

Over the period 2005-2010, testing of imported prawns by AQIS resulted in five samples

positive for chloramphenicol from 269 samples tested, a prevalence of 1.9% (Table 27).

Table 27: Rejection of prawns imported to Australia for presence of chloramphenicol

Country of origin Number of positive samples Concentration (µg/kg)

Vietnam 2 1.1, 0.089

Thailand 2 13, 8.7

Singapore 1 1.2

The concentration used by AQIS for rejection appears to be either <0.3µg/kg or <0.1µg/kg,

though it is noted that one sample was rejected at 0.089µg/kg.

63

An exposure level to consumers from chloramphenicol in prawns was measured by Janssen et

al. (2001) as 0.00000017 mg/kgbw/day.


According to Hanekamp et al. (2003), the Joint FAO/WHO Expert Committee on Food

Additives (JECFA) estimated aplastic anaemia incidence in the order of 1.5 cases per million

people per year, of which about 15% was associated with drug treatment; CAP was not a

major contributor. These data gave an overall incidence of therapeutic CAP-associated

aplastic anaemia in humans of less than one case per 10 million per year.

Regarding epidemiological data derived from the ophthalmic use of CAP, systemic exposure

to this form of treatment was not associated with the induction of aplastic anaemia. There

seems to be no evidence that low-level exposure to CAP, either as a result of ophthalmic use

or of residues in animal food, is related to aplastic anaemia.

Hanekamp et al. (2003) estimate the difference between exposure levels in shrimp and those

encountered in medication as 150,000,000-735,000,000.

4. Risk Characterisation

Janssen et al. (2001) estimated the risk of contracting cancer as a result of consuming shrimp

containing CAP, where concentrations ranged between 1 and 10 µg/kg (ppb) concluding that

the worst-case risk was a 1.1,000,000 added cancer risk in the human population.

References

Hanekamp, J., Frapporti, G. and Olieman, K. 2003. Chloramphenicol, food safety and

precautionary thinking in Europe. Environmental Liability, 11:209-221.

Homan, N. and Padula, D. 2008. SARDI European Union Market Access Program 2007-

2008 Report to the Australian Prawn Farmers Association. South Australian Research and

Development Institute, Urrbrae, South Australia. July 2008.

Janssen, P., Baars, A. and M. Pieters. 2001. Advies met betrekking tot chloramphenicol in

garnalen (Advice regarding chloramphenicol in shrimp). RIVM/CSR, Bilthoven, The

Netherlands.

Lancaster, T., Stewart, A. and Jick, H. 1998. Risk of serious haematological toxicity with use

of chloramphenicol eye drops in a British general practice database. British Medical Journal,

316:667.

http://bmj.bmjjournals.com/cgi/content/full/316/7132/667

http://bmj.bmjjournals.com/cgi/content/full/316/7132/667

64

Sulphite


Sulphur dioxide (220) and sodium and potassium sulphites (221, 222, 223, 224, 228) are

permitted additives to a range of foods in the Australian Food Standards Code. Foods to

which it is permitted to add these anti-browning preservative agents, include alcoholic

beverages, cheeses, various fruit and vegetable products, crustacea, flour products, biscuits

cakes and pastries.

In the case of crustaceans sulphite has long been used to control the development of black

spot (melanosis) in raw prawns and lobsters. Although alternatives such as 4-hexylresorcinol

are available, sulphite remains the agent of choice for controlling black spot.

Levels of sulphur dioxide permitted in crustacea are prescribed in the Food Standards Code

and are 30 µg/kg in cooked crustaceans and 100 µg/kg in uncooked crustaceans. Where the

addition of sulphur dioxide and sodium and potassium sulphites is permitted it must be

declared on the food label.


As part of a longitudinal study of the marine prawn supply chain in Australia Thomas et al.

(2003) measured sulphite levels in prawns caught in South Australia. Of twenty whole prawn

samples measured immediately after dipping in metabisulphite on board the vessel, two had

sulphite levels >100 mg/kg (107 and 140 mg/kg).

Over the period 2005-2010, testing of imported prawns by AQIS resulted in four samples

exceeding the allowable limit. Of 341 samples tested, four (1.2%) exceeded the limit

(Table 28).

Table 28: Rejection of prawns imported to Australia for presence of sulphur dioxide

Country of origin Date Product Concentration (µg/kg)

India 9/2/06 Raw 491

Vietnam 27/4/06 Raw 42*

Vietnam 27/4/06 Cooked 78

Vietnam 8/5/06 Raw 115

* It is not clear why this sample failed; the FSC allows up to 100 mg/kg in raw prawns

It is not known whether whole prawns were tested, or only edible portions of prawn meat,

since the carapace typically contains a much higher level. Hardisson et al. (2002) found that

the sulphite level of prawn meat in Spain and Venezuela varied from 13 to 546 µg/kg (mean

115 µg/kg) while that of carapaces varied from 81 to 8256 µg/kg (mean 2428 µg/kg). Some

samples exceeded the maximum level permitted under European legislation (Directive

95/2/CE) of 150 µg/kg.


A small proportion of the human population, estimated at 14-16% of children and 10-12% of

adults (Asthma Foundation of Victoria), is hypersensitive when exposed to sulphur dioxide or

65

sulphites. For this group, symptoms include asthma, rhinitis (inflammation of the nasal

passages often associated with discharge), rhinoconjunctivitis, urticaria (hives), angio-

oedema (swelling of the tongue and throat), headache, gastrointestinal distress and

anaphylaxis. In challenge studies, reactions in some individuals have been associated with

elevated levels of immunoglobulin E (IgE) indicating a classic atopic allergic reaction, while

in others reactions have occurred without an associated rise in IgE or positive skin prick test

indicating that more than one mechanism is involved in causing symptoms amongst sensitive

individuals (WHO, 1999).

Irritation of the airways by SO2 gas is one possible mechanism (The Australasian Society of

Clinical Immunology and Allergy, accessed 27/7/11). The dose of sulphur dioxide and

sulphites that cause reactions varies according the medical condition of the individual, their

medication and the food type ingested. In one individual, who had suffered severe asthmatic

symptoms on exposure to sulphites in dried apricots and sulphited salad, a few sips of wine

containing sulphites at a concentration of 92 mg/kg caused a fatal anaphylactic reaction

(WHO, 1999). The reporting of adverse reactions to fresh fruit and vegetables, led to a ban on

the use of sulphites on these foods, except potatoes and grapes, in the US in 1986 (WHO,

1999).

No reports of cases of illness associated with consumption of prawns could be found in the

public health literature in Australia (Communicable Diseases Intelligence; State Health

Bulletins).

References

Hardisson, A., Rubio, C., Frias, I., Rodriguez, I. and Reguera, J. 2002. Content of sulphite in

frozen prawns and shrimps. Food Control, 13:275-279.

The Australasian Society of Clinical Immunology and Allergy. 2011. Sulfite Allergy.

http://www.allergy.org.au/content/view/128/146. accessed 27/7/11

Thomas, C., Holds, G. and Pointon, A. 2003. Food safety and quality assurance for green and

cooked prawns: development and evaluation of a framework for the validation of a supply

chain approach. FRDC project no. SIDF 2002/425.

WHO. 1999. WHO Food Additive Series 42 Sulfur Dioxide and Sulfites. Prepared by the

Fifty-first meeting of the Joint FAO/WHO expert committee on food additives (JECFA).

World Health Organization, Geneva.

http://www.allergy.org.au/content/view/128/146

66

Nitrofurans


Nitrofurans are synthetic, broad-spectrum antibacterial drugs used as feed additives for

treatment of gastrointestinal infections in pigs, cattle and poultry. They are also growth

promoters in poultry and prawns when fed at sub-therapeutic levels. Four nitrofurans are used

in feeds, each of which has a metabolite which appears in food products:

Nitrofuran Feed Additive Metabolite (Marker) in Prawns

Furazolidone AOZ (3-amino-oxazolidinone)

Furaltadone AMOZ (3-amino-5- morpholinomethyl-1,3-oxazolidin)

Nitrofurantoin AHD (1-aminohydantoin)

Nitrofurazone SEM (semicarbazide)

Because nitrofurans have been linked with genotoxicity, Australia and the EU prohibited the

use of nitrofurans in feeds in 1992 and 1995, respectively.

In 2003 the Australian Prawn Farmers Association provided evidence to FSANZ that

imported prawns contained nitrofuran residues and nitrofuran metabolites are included in

AQIS’ import testing program.

Recently, it has become known that one metabolite (SEM) occurs naturally in the freshwater

crustacean, Macrobrachium rosenbergii (Poucke et al. 2011). The discovery came about

when it was noted that import testing of M. rosenbergii in Belgium consistently yielded

positive SEM results, with the implication that nitrofurans were being used. The researchers

showed that SEM was synthesised by the prawn and deposited in the carapace, but not in the

meat; positive tests had been carried out on whole prawns.


In 2007, as part of an EU Market Access Program, the South Australian Research and

Development Institute (SARDI) undertook residue testing of prawns in conjunction with the

Australian Prawn Farmers Association (APFA). All samples of prawns from six prawn farms

had AHD, AMOZ and AOZ levels below the laboratory limit of detection (0.2 µg/kg) and

SEM levels were also below the limit of detection of 0.4 µg/kg (Homan & Padula, 2008).

Over the period 2005-2010, testing of imported prawns by AQIS resulted in 62 samples

positive for nitrofuran metabolites from 1,741 samples tested, a prevalence of 3.6%; Chinese

prawns tested positive on 36 occasions and Indian prawns on 26 occasions.

The designation of positives according metabolite is presented in Table 29 from which it can

be seen that the four marker metabolites were detected in approximately similar proportions

(18 described as ‘nitrofurans’ were probably misnamed). Concentrations of positive samples

varied from ‘not detected’ (which would benefit from clarification) to 8.2 µg/kg ‘nitrofuran’.

Exposure of prawn consumers to AOZ was determined by FSANZ (2005). The mean

exposure ranged from 0.0009-00.19 µg/kgbw/day and that for ‘high-end’ consumers from

0.003-0.0064 µg/kgbw/day.

67


In 1993, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) concluded that:

Furazolidone (AOZ) was a genotoxic carcinogen, based on increased incidence of

malignant tumours in mice and rats

Nitrofurazone (SEM) produced tumours (benign) in rats and mice

No acceptable daily intake (ADI) for furazolidone or nitrofurazone was advocated.


When FSANZ compared the upper bound for consumption by ‘high-end’ prawn consumers

with doses shown to cause tumours in laboratory animals there was a 4,000,000-times

difference; for ‘average’ consumption of prawns the difference was 12,000,000-times.

FZANZ concluded that the food safety risk from consumption of prawns containing

nitrofuran residues was very low.

Table 29: Rejection of prawns imported to Australia for presence of nitrofuran residues

Metabolite Number of positive samples

AHD 11

AMOZ 11

AOZ 12

SEM 10

‘Nitrofurans’ 18

Hanekamp et al. (2003) has noted that SEM is found in several sources other than animal

feeds: plastic gaskets for glass jars, plant and animal matrices which had been dried, food

samples treated with hypochlorite. These sources are in addition to the finding of Poucke et

al. (2011) that SEM is a natural component of the carapace of at least one prawn in

international trade.

References

FSANZ. 2005. Nitrofurans in prawns: a toxicological review and risk assessment. Technical

report series No 31. Canberra, Australia.

Hanekamp, J., Frapporti, G. and Olieman, K. 2003. Chloramphenicol, food safety and

precautionary thinking in Europe. Environmental Liability, 11:209-221.

Homan N. and Padula D. 2008. SARDI European Union Market Access Program 2007-2008

Report to the Australian Prawn Farmers Association. South Australian Research and

Development Institute, Urrbrae, South Australia. July 2008.

Poucke, C, Detaverniert, C., Wille, M., Kwakman, J., Sorgeloos, P. and van Peteghem, C.

2011. Investigation into the possible natural occurrence of semicarbazide in Macrobrachium

rosenbergii prawns. Journal of Agricultural and Food Chemistry, 59:2107-2112.

68

Cadmium


In 1972, the Joint FAO/WHO Expert Committee on Food Additives and Contaminants

(JEFCA) established a Provisional Tolerable Weekly Intake (PTWI) for cadmium of 400-

500 μg per person, approximately 7-8 μg/kg per body weight per week (bw/w) and 60-70 μg

per day for a 60 kg person.

In 1993, JEFCA introduced a safety factor, advising a reduction in the PTWI to

7 μg/kg bw/w, a level confirmed in 1995 by the European Commission and reconfirmed by

JEFCA in 2003.

Cadmium can enter cells and bind with ligands; it is not easily cleared by the body and has a

long residence time (half-life 10-30 years) in organs such as liver, kidney and the intestine.

Cadmium has been associated with disorders of the kidneys, bones and nervous system, and

is also identified as a carcinogen.

The EU set maximum levels (MLs) for foodstuffs, including seafood, based on the results of

a dietary exposure assessment and the opinions of JEFCA (Table 30). Full details of the

scientific underpinning is contained in a risk assessment carried out by EFSA (EFSA. 2009).

Table 30: Maximum levels for cadmium in seafood (EFSA. 2009)

Product ML (mg/kg)

Muscle meat of fish, excluding certain species listed below 0.05

Bonito (Sarda sarda)

Common two-banded seabream (Diplodus vulgaris)

Eel (Anguilla anguilla)

Grey mullet (Mugil labrosus labrosus)

Horse mackerel or scad (Trachurus spp)

Louvar or luvar (Luvarus imperialis)

Mackerel (Scomber spp)

Sardine (Sardina pilchardus)

Sardinops (Sardinops spp)

Tuna (Thunnus spp, Euthynnus spp, Katsuwonus pelamis)

Wedge sole (Dicologoglossa cuneata)

0.10

Muscle meat of bullet tuna (Auxis spp) 0.20

Muscle meat of anchovy (Engraulis spp)

Swordfish (Xiphias gladius)

0.30

Crustaceans, excluding brown meat of crab and excluding head and

thorax meat of lobster and similar large crustaceans (Nephropidae and

Palinuridae)

0.50

Bivalve molluscs 1.0

Cephalopods (without viscera) 1.0

Cadmium is a perceived hazard in the European Union and affects only exports to that

market.

69


The issue in the Australian context is that, within a lot of production of prawns, a proportion

may contain cadmium in excess of the ML (0.5 mg/kg).

Over the period 2001-2011 the EU, via its Rapid Alert system, has rejected 133 consignments

of crustaceans on the basis of the ML.

Among the rejections were 39 consignments of Australian frozen prawns with cadmium

levels up to 2 mg/kg, reflecting the bioaccumulation of the metal by prawns in certain

Australian waters.

Based on ABARE data, the volume of prawns exported from Australia to Europe has

diminished significantly in the aftermath of the rejections (Table 31).

A detailed listing of cadmium levels in Australian prawns is presented in Anon. (2007).

Table 31: Exports of prawns from Australia to the EU (2005-2009)

2005-06 2006-07 2007-08 2008-09

Export volume (t) to EU 2,666 1,316 548 340

Total exports (t) 8,744 6,376 4,916 4,797

Proportion (%) exported to EU 30.5 20.6 11.2 7.1

Value ($,000) 39,205 17,825 7,537 3,600

Total exports ($,000) 133,923 93,563 68,624 82,180

Proportion (%) exported to EU 34.4 19.1 11.0 4.4


Food represents the major source of cadmium exposure, with moderate smoking another

major source. Toxicity in the kidney is progressive and requires many years of accumulation

with a concentration in the renal cortex of 200 mg/kg at age 50 accepted as a critical

concentration at which kidney damage may be manifested in susceptible individuals.

Detailed expositions of cadmium toxicity are contained in Anon. (2007) and EFSA (2009).


In 2007, the Australian government (Anon. 2007) made a submission to the European

Commission to review the ML for crustaceans citing, as evidence for its deletion that:

The Codex Alimentarius Commission had set no ML for cadmium in crustaceans, on

the basis that crustaceans represent a minor exposure to cadmium.

While median levels for prawns in Australia’s export trade were 0.11 mg/kg (range

0.01-0.15 mg/kg) the distribution is highly skewed and a proportion could not meet

the ML criterion at the 95th

percentile.

Australian prawns do not contribute significantly to the cadmium ingested by

European consumers.

70

References

Anonymous. 2007. Australian government submission to the European Commission to

review the cadmium maximum limit in crustaceans. Canberra.

EFSA. 2009. Scientific opinion: Cadmium in food. Scientific opinion of the panel on

contaminants in the food chain. EFSA Journal 908:1-39.

71

TOR 3: Risk Assessment of Identified Hazards

Three types of risk assessments can potentially be used to provide an estimate of illness

associated with consumptions of prawns:

Qualitative risk assessment

Semi-quantitative risk assessment

Quantitative risk assessment

Choosing which type of assessment to carry out is influenced primarily by the requirements

of the risk manager and secondarily by the availability of data which will inform the

assessment. Unless there are extremely pressing reasons for undertaking it, a full quantitative

risk assessment is not done. Such assessments are expensive and time-consuming, for

example the USA risk assessment of E. coli O157 in hamburgers.

In this study a qualitative tool will be used where data are scarce and a semi-quantitative tool

(Risk Ranger) where data allow. As well, where quantitative risk assessments have been done

their outputs will be integrated into the study.

3.1 Qualitative Risk Assessment Tool

A qualitative framework for the rating of risk has been used based on premises published by

the International Commission on Microbiological Specifications of Foods (ICMSF, 2002)

and by Food Science Australia (FSA, 2000). The ICMSF formulated descriptors for severity

of illnesses caused by various pathogens and these are used in conjunction with a matrix of

factors assembled by FSA (2000) for use in risk profiling.

Taken together, the present qualitative matrix is based on criteria for:

Severity

The severity of the identified hazards was classified according to the International

Commission of the Microbiological Specifications of Food (ICMSF 2002) with level of

severity defined as follows:

IA. Severe hazard for general population; life threatening or substantial chronic sequelae or

long duration.

IB. Severe hazard for restricted populations; life threatening or substantial chronic sequelae

or long duration.

II. High hazard; incapacitating but not life threatening, sequelae rare, moderate duration.

III. Moderate; not usually life threatening, no sequelae, normally short duration, symptoms

are self limiting, can be severe discomfort.

Occurrence of illness

This is classified as low, medium or high based on the hazard’s involvement as recorded in

public health statistics.

Growth

An indication is given of whether growth of the pathogen in the product is required to cause

72

disease. In general, microbiological hazards need to grow in the product or be present at high

numbers before there is a significant risk of disease.

In the case of chemicals such as heavy metals where chronic exposure is needed over a

protracted period, for the purposes of the qualitative risk assessment, the situation is

considered analogous to that of growth.

Production, processing or handling of food

The production, processing or handling of the food may increase, decrease or not affect the

concentration of the hazard.

Consumer terminal step

This element considers whether a consumer terminal step, such as cooking, is applied to the

product. Cooking by the consumer will, for most biological hazards, reduce the subsequent

risk of disease.

Epidemiology

Consideration is given as to whether the hazard-commodity combination has been recorded

as a cause of food poisoning.

3.2 Semi-Quantitative Risk Assessment Tool - Risk Ranger

In 2000, Huss et al. published a framework which proved useful for making a qualitative risk

assessment. There were six criteria:

Bad safety record

No CCP for the hazard

Possibility of contamination or recontamination

Abusive handling possible

Growth of pathogens can occur

No terminal heating step

The authors provided examples of how the tool could be used for a range of seafood products

and the framework was the basis for development of a semi-quantitative took, Risk Ranger

(Ross & Sumner, 2002), which was used for the national seafood risk assessment in Australia

(Sumner & Ross, 2002).

Risk Ranger incorporates all factors that affect the risk from a hazard in a particular

commodity including:

Severity of the hazard and susceptibility of the population of interest

Likelihood of a disease-causing dose of the hazard being present in a meal

Number of meals consumed by a population of interest in a given period of time

A number of factors affect each of the above.

73

Disease severity is affected by:

a) Intrinsic features of the pathogen/toxin

b) Susceptibility of the consumer.

Exposure to the food will depend on how much is consumed by the population of interest,

how frequently they consume the food and the size of the population exposed.

Probability of exposure to an infectious dose will depend on:

a) Serving size

b) Probability of contamination in the raw product

c) Initial level of contamination

d) Probability of contamination at subsequent stages in the catching-processing-

distribution chain

e) Changes in the level of the hazard during the chain, including concentration or

dilution, growth or inactivation of hazard.

Risk Ranger has a ‘shopfront’ with a list of boxes into which are entered information using

the computer’s mouse. In total, there are eleven questions and a mathematical model then

converts each answer to a numerical value or ‘weighting’ - the weightings are detailed in the

paper by Ross and Sumner (2002). Some of the weightings are arbitrary, while others are

based on known mathematical relationships e.g. from days to weeks, or years. To help make

responses as objective as possible and to maintain transparency of the model, descriptions are

provided and many of the weighting factors are specified. As well, in some cases, if the

options provided don’t accurately reflect the situation being modelled, a numerical value can

be entered using ‘Other’.

Behind the shopfront is the model, developed in Microsoft Excel software, using standard

mathematical and logical functions. The list box macro tool is used to automate much of the

conversion from qualitative inputs to quantities for calculations. For each selection made

from the range of options, the software converts that selection into a numerical value.

Outputs

Risk Ranger combines the factors in Questions 1-11 including some logical tests to generate

two estimates of risk:

Risk Ranking – a score between 0-100

Predicted annual illnesses in the population selected

Full details of the logic and equations leading to the risk estimates are shown in the paper by

Ross and Sumner (2002).

Risk ranking

The Risk Ranking value is scaled logarithmically between 0 and 100. The former is equated

to a probability of foodborne illness of less than, or equal to, one case per 10 billion people

(greater than current global population) per 100 years. At the upper limit (Risk

Ranking=100), every member of the population eats a meal that contains a lethal dose of the

hazard every day. A Risk Ranking change of 6 corresponds to a 10-fold difference in the

74

absolute risk. Thus an increase in Risk Ranking from 36 to 48 means that the risk increased

100-times.

Predicted annual illness

Risk Ranger estimates the total number of illnesses in the population selected at Question 5.

Obviously, the higher the risk ranking, the greater the proportion of the population will

become ill. The absolute numbers of illnesses, however will depend on the population size.

3.3 Identified Hazards

Based on TOR 1, the following hazards have been identified.

Biological Hazards Risk Assessment Carried Out

Vibrio parahaemolyticus Qualitative Semi-quantitative

Vibrio cholerae Qualitative Semi-quantitative

Salmonella Qualitative Semi-quantitative

Hepatitis A None

Chemical Hazards

Sulphite Qualitative

Cadmium Qualitative

Chloramphenicol Qualitative

Nitrofurans Qualitative

Qualitative risk assessments were carried out on all identified hazards, with the exception of

Hepatitis A in imported prawns, for which there were insufficient data.

Where there were sufficient data, a semi-quantitative risk assessment was undertaken e.g. on

Vibrio spp and Salmonella in prawns. Because of significant data gaps, it was only possible

to undertake qualitative risk assessments for chemical hazards.

References

Food Science Australia. 2000. Final Report – Scoping study on the risk of plant products.

SafeFood NSW, Homebush, NSW, Australia.

Huss, H.H., Reilly, A. and Ben Embarek, P.K. 2000. Prevention and control of hazards in

seafoods. Food Control, 11, 149-156.

ICMSF. 2002. Microorganisms in Foods: 7 Microbiological testing in food safety

management. New York, NY, United States of America: Kluwer Academic/Plenum

Publishers.

Ross, T. and Sumner, J. 2002. A simple, spreadsheet-based, food safety risk assessment tool.

International Journal of Food Microbiology, 77, 39-53.



75

TOR 4: Risk Assessment of Hazard:Product Pairings

4.1 Risk Assessment: Vibrio cholerae

Two scenarios are considered:

1. Raw prawns are eaten raw, as sashimi

2. Raw prawns are stored, cooked and consumed in accordance with the Food Standards

Code either in the home or in the food service sector

For each scenario a qualitative and semi-quantitative risk analysis is made.

Data inputs to Risk Ranger are based on data accumulated by the joint FAO-WHO panel

which worked on ‘Vibrios in seafood’ (Anon. 2005).

4.1.1 Qualitative assessment of the risk of contracting cholera from imported warm-water prawns

The following assumptions are made:

1. 90% of servings are consumed cooked and 10% consumed raw

2. Imports of prawns are around 20,000,000 kg/annum

3. An average serving size is 200 g

4. Total number of serves is 100,000,000/annum, of which 10 million are consumed raw

and 90 million cooked.

5. The population is 23 million

AQIS import testing has detected V. cholerae in 13/498 (2.6%) of samples of cooked,

imported prawns over the period 2005-11, there was no further analysis to determine whether

any isolate was toxigenic.

However, the likelihood of being exposed to an infectious dose of choleragenic V. cholerae

through the consumption of imported warm-water prawns is extremely low, based on the data

presented in the hazard sheet, which indicates only two isolations of choleragenic V. cholerae

in more than 20,000 port-of-entry analyses of imported warm water prawns.

A matrix embracing responses to the above qualitative criteria is presented (Table 31) from

which it can be seen that, in qualitative terms, the risk of contracting cholera from

consumption of warm-water prawns, whether eaten raw or cooked, is very low.

76

Table 31: Microbiological hazard risk rating for choleragenic V. cholerae in prawns imported to Australia (after ICMSF 2002 and FSA 2000)

Product Identified

hazard

Severity1 Occurrence

of illness2

Growth in

product

required to

cause disease

Prodn/process/handling

hazard3

Consumer

terminal

step4

Epidemiological

link

Risk

Rating

Raw prawns Choleragenic

V. cholerae

II Very low Yes Inactivation during

washing, icing, freezing

No No Very

low

Prawns

cooked at the

plant and

eaten without

further heat

treatment

Choleragenic

V. cholerae


washing, icing, cooking

(optional), freezing

No No

Very

low

Prawns

cooked

immediately

before

consumption

Choleragenic

V. cholerae


washing, icing, (optional),

freezing, thawing and

cooking

Yes No

Very

low

1 Severity level II refers to the severity of the identified hazard as classified according to the International Commission of the Microbiological Specifications of Food (ICMSF

2002). Level II: High hazard; incapacitating but not life threatening; sequelae rare; moderate duration. 2 Very low occurrence of illness can, for the purposes of this risk assessment, be described as an average of less than I case per 10 million population per year based on the

data that was available over a 6 year period (see hazard sheet) 3 As the level of inactivation for processing is in the range of a 5-6 log reduction and the initial contamination level less than 1 in 25g, the likelihood of having choleragenic

V. cholerae in the prawns after cooking was considered to be very low. 4 Cooking of prawns also brings about a 5 - 6 log reduction in the level of V. cholerae, thus the likelihood of having choleragenic V. cholerae in the prawns after processing

was considered to be very low.

77

4.1.2 Semi-quantitative risk of contracting cholera from imported warm-water prawns

Question 1. Hazard Severity

Risk Ranger alternative: ‘MODERATE hazard - requires medical intervention in most cases’

was chosen as the response to Question 1.

Question 2. How susceptible is the population of interest

For the current assessment: ‘GENERAL - all members of the population’ was selected.

Questions 3 and 4: Frequency of consumption and proportion consuming






and 90 million cooked


6. 25% of the population consumed prawns raw twice/annum (a few times per year)

7. 25% of population consumed cooked prawns once a month

Question 5. Size of consuming population

Population is 23,000,000.

Question 6. Probability of contamination of raw product per serving

Dalsgaard et al. (1995a) found that V. cholerae O1 was present in 2% (2/107) of water,

sediment and prawns samples collected from a major prawn culture area in South-east Asia

though testing of isolates indicated absence of the ctx genes in both the O1 strains (Dalsgaard

et al. 1995b). Data from India showed the presence of V. cholerae O1 in 0.2% of raw prawns

(Ministry of Agriculture, India). However, the choleragenic status of these prawn-associated

strains is unknown. Data submitted to FAO/WHO from Argentina (personal communication

M. Costagliola, 2001) indicate the absence of V. cholerae O1 and O139 in 400 prawn and 15

water samples examined. Based on this information probability of contamination of incoming

prawns was considered RARE (0.1%).While not stated, implicit at Question 6 is the need to

estimate a concentration of V. cholerae on incoming prawns. In the absence of any

information a premise used by other researchers which, at its simplest, states that, if the

prevalence is low, the concentration is also likely to be low, has been used. While some risk

assessments (Bemrah et al. 1999) have noted that pathogens are probably heterogeneously

distributed in some foods, all to date have assumed that pathogens present in foods are

distributed homogeneously. This is clearly a simplification.

In the present study, a concentration of 10 cfu/g was used (the limit of detection) equivalent

to 2000 cfu/serve. This concentration is used to answer question 10 (increase to infectious

dose) for prawns consumed raw.

78

Question 7. Effect of Processing

Data in the hazard sheets for V. cholerae illustrate the effect of processing on inactivation of

V. cholerae for which a >5 log inactivation is documented during washing, icing and

freezing. For Question 7 the alternative: USUALLY ELIMINATES is selected. Based on the

information presented in the hazard sheet this is an extremely conservative estimation.

If prawns are cooked during processing the lethality of the temperature:time regimes used in

the industry are greatly in excess of 6 log units which leads to selection that the hazard is

RELIABLY ELIMINATED at this stage.

Question 8. Recontamination

Given the description of processing in the international trade (see hazard sheet),

recontamination was considered not to occur.

Question 9. Effectiveness of Post-processing Controls

The cold chain in international trade (frozen and chilled) is well established and V. cholerae

has a temperature minimum for growth of 10°C (see hazard sheet) and the Risk Ranger

alternative: WELL CONTROLLED (no increase in population) has been selected.

Question 10. Increase in the post-processing contamination level that would cause

infection or intoxication to the average consumer.

From consideration of dose response (See hazard sheet) and the data of Levine et al. (1981),

Tauxe et al. (1994), Health Canada (2001) and FDA/CFSAN (2003), a dose of 1 million (106)

V. cholerae was selected. In a serving of 200 g such an ID50 is equivalent to a concentration

approximately 3000 cfu/g of prawns at the point of consumption. To answer question 10 it is

necessary to divide the level at Q6 from the level for an infective dose. In this case:

Q10 = 106

Q6 = 103 (200g serve with concentration 10 cfu/g = 2000 g/serve)

The difference is approximately 103

and this value is used at Question 10 in connection with

consumption of raw prawns.

Question 11. Effect of preparation before eating

Where prawns are cooked it is likely that this will result in complete elimination of

V cholerae. The organism is not heat tolerant and the location of the site of microbiological

concern as the carapace means that heat treatment will be immediate. Thus any form of

cooking (steaming, boiling or barbecuing) will result in complete elimination.

Where prawns are eaten raw there is no effect on the hazard.

4.1.3 Risk ratings, predicted illnesses and reality check

In Table 32 are presented risk ratings and predicted illnesses based on consumption of raw

and cooked imported prawns.

For prawns consumed raw, risk of illness has a rating of 28 with 1.7 illnesses every decade.

In assessments of paired seafood hazard:products pairings in Australia. Sumner and Ross

(2002) found that Risk Ranger ratings <30 were not equated with any reports of illness.

79

For prawns consumed cooked, the hazard is reliably eliminated during cooking either at the

plant level (Risk Ranger Question 7: Reliably eliminates) or during meal preparation (Risk

Ranger Question 11: Reliably eliminates). This leads to Risk Ranger rating of 0 and

prediction of no illnesses.

Thus, a semi-quantitative assessment of the likelihood of contracting cholera from

consumption of warm-water prawns by consumers in major importing countries is of the

order of two cases/decade.

It should be noted that the joint FAO-WHO expert panel undertook a quantitative risk

assessment of consumption of warm-water prawns by major importing countries. Median risk

of contracting cholera from consuming prawns raw varied from two cases/century in several

European countries to four cases/decade in the USA.

Based on the above, the likelihood of contracting cholera from consumption of raw imported

prawns is extremely low.

Table 32: Estimation of risk of cholera associated with consumption of imported warm-water prawns in Australia

Risk criteria Prawns consumed raw Prawns consumed cooked

Dose and severity

Hazard severity Moderate Moderate

Susceptibility General – all population General – all population

Probability of exposure

Frequency of consumption Few times a year Monthly

Proportion consuming Some (25%) Some (25%)

Size of population 23 million 23 million

Probability of contamination

Probability of raw product

contaminated

0.1% (10 cfu/g) 0.1% (10 cfu/g)

Effect of processing 2-log inactivation 2-log inactivation

Possibility of recontamination None None

Post-process control Well controlled Well controlled

Increase to infective dose 1000x 1000x

Further cooking before heating No effect Reliably eliminates hazard

Predicted illnesses/decade 1.7 0

Risk ranking (0-100) 28 0

References

Anonymous. 2005. Risk assessment of choleragenic Vibrio cholerae O1 and O139 in warm-

water shrimp in international trade. FAO/WHO Microbiological risk assessment series 9

(2005).

Bemrah, N., Sara, M., Cassin, M., Griffiths, M., Cerf, O., 1999. Quantitative risk assessment

of human listeriosis from consumption of soft cheese made from raw milk. Prevent. Vet.

Med. 37, 129-145.

80

Dalsgaard, A., Huss, H.H., H-Kithikun, A. and Larsen, J.L. 1995a. Prevalence of Vibrio

cholerae and Salmonella in a major shrimp production area in Thailand. Int. J. Food

Microbiol. 28: 101-113.

Dalsgaard, A., Serichantalergs, O., Shimada, T., Sethabuthr, O. and Echeverria, P. 1995b.

Prevalence of Vibrio cholerae with heat-stable enterotoxin (NAG-ST) and cholera toxin

genes: restriction fragment length polymorphisms (RFLP) of NAG-ST genes among

V. cholerae O serogroups from a major shrimp production area in Thailand. J. Med.

Microbiol, 43: 216-220.

FDA, CFSAN. 2003. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. The

‘Bad Bug Book’. Available at http://vm.cfsan.fda.gov/~mow/intro.html



Health Canada. 2001.Material Safety Data Sheet – Infectious substances Available at

http://www.phac-aspc.gc.ca/msds-ftss/msds164e.html



Publishers.

Levine, M.M., Black, R.E., Clements, M.L., Nalin, D.R., Cisneros, L. and Finkelstein, R.A.

1981. Volunteer studies in development of vaccines against cholera and enterotoxigenic

Escherichia coli: a review. In: Holme, J. et al. (eds) Acute enteric infections in children. New

prospects for treatment and prevention. Elsevier/North Holland Biomedical Press,

Amsterdam. pp. 443-459



Tauxe, R.V., Blake, P., Olsvik, O. and Wachsmuth, K.I. 1994. The future of cholera:

Persistence, change and an expanding research agenda. In: Vibrio cholerae and cholera.

Wackmuth, K.I., Blake, P.A. and Olsvik, O. (eds). American Society for Microbiology,

Washington, DC. Pp. 443-453.


81

4.2 Risk Assessment: Vibrio parahaemolyticus






Data inputs to Risk Ranger are based on data accumulated by the joint FAO-WHO panel

which worked on ‘Vibrios in seafood’ (Anon. 2011).

4.2.1 Qualitative assessment of the risk of illness from V. parahaemolyticus in imported warm-water prawns







5. The Australian population is 23 million

Based on information presented in hazard sheets for reduction of V. cholerae and

V. parahaemolyticus populations during processing, the likelihood of being exposed to an

infectious dose of toxigenic V. parahaemolyticus through the consumption of imported

warm-water prawns is extremely low.


which it can be seen that, in qualitative terms, the risk of contracting illness from toxigenic

V. parahaemolyticus from consumption of warm-water prawns, whether eaten raw or cooked,

is very low.

While there were two instances (1990, 1992) where prawns imported from Indonesia were

implicated in food poisoning outbreaks in NSW (Kraa, 1995) it is understood that

temperature abuse at the retail and caterer levels was the cause.

82

Table 33: Microbiological hazard risk rating for toxigenic V. parahaemolyticus (Vp) in prawns imported to Australia (after ICMSF 2002, FSA 2000)

Product Identified

hazard


of illness2

Growth in

product

required to

cause

disease


hazard3

Consumer

terminal

step4

Epidemiological

link5

Risk

Rating

Raw prawns Toxigenic

Vp

III Very low Yes Inactivation during


No No Very

low

Prawns

cooked at the

plant and

eaten without

further heat

treatment

Toxigenic

Vp

III

Very low Yes Inactivation during



No Yes

Very

low

Prawns

cooked

immediately

before

consumption

Toxigenic

Vp

III




cooking

Yes No

Very

low

1 Severity level III refers to the severity of the identified hazard as classified according to the International Commission of the Microbiological Specifications of Food

(ICMSF 2002). Level III: Moderate; not usually life threatening, no sequelae, normally short duration, symptoms are self limiting, can be severe discomfort. 2 Very low occurrence of illness can is based on a lack of cases of illness for almost two decades.

3 As the level of inactivation for processing is in the range of a 5-6 log reduction and the initial contamination level less than 10/g, the likelihood of having toxigenic

V. parahaemolyticus in prawns after processing was considered to be very low. 4 Cooking of prawns also brings about a 5-6 log reduction in the level of V. parahaemolyticus, thus the likelihood of having toxigenic V. parahaemolyticus in prawns after

processing was considered to be very low. 5 Two outbreaks of illness in which V. parahaemolyticus was implicated are described in the Hazard Sheet for V. parahaemolyticusof this report (Kraa, 1995).

83

4.2.2 Semi-quantitative risk of contracting V. parahaemolyticus illness from imported warm-water prawns


Risk Ranger alternative: ‘Mild hazard – sometimes requires medical intervention’ was chosen

as the response to Question 1.
















There have been two outbreaks of food poisoning due to the presence of V. parahemolyticus

in imported, cooked prawns (Kraa, 1995). Based on this information probability of

contamination of incoming prawns was considered RARE (0.1%).

While not stated, implicit at Question 6 is the need to estimate a concentration of

V. parahaemolyticus on incoming prawns. In the absence of any information a premise used

by other researchers which, at its simplest, states that, if the prevalence is low, the

concentration is also likely to be low, has been used. While some risk assessments (Bemrah

et al. 1999) have noted that pathogens are probably heterogeneously distributed in some

foods, all to date have assumed that pathogens present in foods are distributed

homogeneously. This is a clearly a simplification.

In the present study, a concentration of 10 cfu/g was used (the limit of detection) equivalent

to 2000 cfu/serve. This concentration is used to answer Question 10 (increase to infectious

dose) for prawns consumed raw.


Data in the hazard sheets for Gram-negative bacteria illustrate the effect of processing on

inactivation of vibrios for which a >5 log inactivation is documented during washing, icing

and freezing; a similar level of inactivation is assumed for V. parahaemolyticus. For

84

Question 7 the alternative: USUALLY ELIMINATES is selected. Based on the information

presented in the hazard sheet this is an extremely conservative estimation.








The cold chain in international trade (frozen and chilled) is well established and

V. parahaemolyticus has a temperature minimum for growth of 5°C (see hazard sheet) and

the Risk Ranger alternative: WELL CONTROLLED (no increase in population) has been

selected.



The USA risk assessment on V. parahaemolyticus (FDA, CFSAN, 2005) indicates that a dose

of 1,000,000 cells corresponded to a probability of disease around 10%. In line with this dose

level, oysters in the United States are permitted a maximum of 10,000 V. parahaemolyticus/g

– equivalent to 1,000,000 cells in a 100 g serving of flesh.

To answer question 10 it is necessary to divide the level at Q6 from the level for an infective

dose. In this case:

Q10 = 106

Q6 = 103 (200 g serve with concentration 10 cfu/g = 2000 g/serve)






V. parahaemolyticus. The organism is not heat tolerant and the location of the site of

microbiological concern as the carapace means that heat treatment will be immediate. Thus

any form of cooking (steaming, boiling or barbecuing) will result in complete elimination.





For prawns consumed raw, the risk of illness has a rating of 22 with 1.5 illnesses every

decade. In assessments of paired seafood hazard:products pairings in Australia. Sumner and

Ross (2002) found that Risk Ranger ratings <30 were not equated with any reports of illness.

85

For prawns consumed cooked, the hazard is reliably eliminated during cooking either at the




Thus, a semi-quantitative assessment of the likelihood of contracting illness from

V. parahaemolyticus following consumption of warm-water prawns by consumers in major

importing countries is of the order of 1-2 cases/decade.

Table 34: Estimation of risk associated with consumption of imported warm-water prawns in Australia


Dose and severity

Hazard severity Mild Mild








contaminated

0.1% (10 cfu/g) 0.1% (10 cfu/g)




Increase to infective dose 1,000x 1,000x




References

Anonymous. 2011. Risk assessment of Vibrio parahaemolyticus in oysters. FAO/WHO

Microbiological risk assessment series (in press).



Med. 37, 129-145.

FDA, CFSAN. 2003. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. The

‘Bad Bug Book’. Available at http://vm.cfsan.fda.gov/~mow/intro.html





Publishers.


86


Australia 47(9), 418-423.



87

4.3 Risk Assessment: Salmonella






Data inputs to Risk Ranger are informed by the FAO export workshop on the application of

biosecurity measures to control Salmonella contamination in sustainable aquaculture (Anon.

2010).

4.3.1 Qualitative assessment of the risk of illness from Salmonella in imported warm-water prawns







5. The Australian population is 23 million

Based on information gathered by the joint FAO-WHO panel on reduction of Gram-negative

populations during processing, the likelihood of being exposed to an infectious dose of

Salmonella through the consumption of imported warm-water prawns is extremely low.

There has been one recall (2004) of cooked prawns (FSANZ recall data).

Testing of imported prawns by AQIS did not isolate Salmonella from 473 samples of cooked,

imported prawns.


which it can be seen that, in qualitative terms, the risk of contracting salmonellosis from

consumption of warm-water prawns, whether eaten raw or cooked, is very low.

88

Table 35: Microbiological hazard risk rating for Salmonella in prawns imported to Australia (after ICMSF 2002, FSA 2000)

Product Identified

hazard


of illness2

Growth in

product

required to

cause

disease


hazard3

Consumer

terminal

step4

Epidemiological

link

Risk

Rating

Raw prawns Salmonella II Very low Yes Inactivation during


No No Very

low

Prawns

cooked at the

plant and

eaten without

further heat

treatment

Salmonella II




No No

Very

low

Prawns

cooked

immediately

before

consumption

Salmonella II




cooking

Yes No

Very

low

1 Severity level II refers to the severity of the identified hazard as classified according to the International Commission of the Microbiological Specifications of Food (ICMSF

2002). Level II: High hazard; incapacitating but not life threatening, sequelae rare, moderate duration. 2 Very low occurrence of illness can is based on a lack of cases of illness for almost two decades.

3 As the level of inactivation for processing is in the range of a 5-6 log reduction and the initial contamination level less than 10/g, the likelihood of having Salmonella in

prawns after processing was considered to be very low. 4 Cooking of prawns also brings about a 5-6 log reduction in the level of Salmonella, thus the likelihood of having Salmonella in prawns after processing was considered to

be very low.

89

4.3.2 Semi-quantitative risk of contracting Salmonella illness from imported warm-water prawns


Risk Ranger alternative: ‘Mild hazard – sometimes requires medical intervention’ was chosen

as the response to Question 1.
















Apart from one recall of imported prawns, Salmonella has not been isolated from almost 500

samples of imported, cooked prawns by AQIS testing. Based on this information, the

probability of contamination of incoming prawns was considered RARE (0.1%).

While not stated, implicit at Question 6 is the need to estimate a concentration of Salmonella

on incoming prawns. In the absence of any information a premise used by other researchers

which, at its simplest, states that, if the prevalence is low, the concentration is also likely to

be low, has been used. While some risk assessments (Bemrah et al. 1999) have noted that

pathogens are probably heterogeneously distributed in some foods, all to date have assumed

that pathogens present in foods are distributed homogeneously. This is a clearly a

simplification.

In the present study, a concentration of 1 cfu/g was used, equivalent to 200 cfu/serve. This

concentration is used to answer Question 10 (increase to infectious dose) for prawns

consumed raw.


Data in the hazard sheets for Salmonella illustrate the effect of processing on inactivation of

Gram-negatives, for which a >5 log inactivation is documented during washing, icing and

90

freezing. For Question 7 the alternative: USUALLY ELIMINATES is selected. Based on the

information presented in the hazard sheet this is an extremely conservative estimation.








The cold chain in international trade (frozen and chilled) is well established and Salmonella

has a temperature minimum for growth of 7°C (see hazard sheet) and the Risk Ranger

alternative: WELL CONTROLLED (no increase in population) has been selected.



It is difficult to establish a dose response model for Salmonella because:

There are more than 2,000 serovars with widely differing pathogenicity

Some foods (with high fat) facilitate passage of the pathogen through the strongly-

acidic conditions of the stomach

Consumers vary in their immune status

Several dose response curves have been developed over recent years for various non-

typhoidal Salmonella. In general, an ingested dose around 104 cells has little probability of

causing disease, while 108 cells are likely to cause infection in 80% of consumers.

For the purpose of the present assessment an infective dose of 106 cells was used.

To answer question 10 it is necessary to divide the level at Q6 from the level for an infective

dose. In this case:

Q10 = 106

Q6 = 102 (200 g serve with concentration 1 cfu/g = 200 g/serve)






Salmonella. The organism is not heat tolerant and the location of the site of microbiological

concern as the carapace means that heat treatment will be immediate. Thus any form of

cooking (steaming, boiling or barbecuing) will result in complete elimination.


91




For prawns consumed raw, risk of illness has a rating of 16 with 1.5 illnesses every century.

In assessments of paired seafood hazard:products pairings in Australia. Sumner and Ross

(2002) found that Risk Ranger ratings <30 were not equated with any reports of illness.

For prawns consumed cooked the hazard is reliably eliminated during cooking either at the




Thus, a semi-quantitative assessment of the likelihood of contracting illness from Salmonella

following consumption of warm-water prawns by consumers in major importing countries is

of the order of 1-2 cases/century.

Table 36: Estimation of risk of contracting salmonellosis following consumption of imported warm-water prawns in Australia


Dose and severity

Hazard severity Mild Mild








contaminated

0.1% (1 cfu/g) 0.1% (1 cfu/g)




Increase to infective dose 10,000x 10,000x




References

Anonymous. 2010. Report of the FAO expert workshop on the application of biosecurity

measures to control Salmonella contamination in sustainable aquaculture. Mangalore, India.



Med. 37, 129-145.

92





Publishers.



93

4.4 Risk Assessment of Chemical Hazards

For several reasons, achieving a useful assessment of risk from ingesting chemicals contained

in prawns is difficult because:

There are no recorded cases of illness associated with the hazard:product pairing.

Chronic exposure over many years may be required for adverse reaction (e.g. cadmium

intake and kidney disease).

Risk of exposure are considered dose-independent e.g. any dose of chloramphenicol and

nitrofurans is considered by some authorities (EU) to be disease-causing at any dose

The application of ‘zero tolerance’, with its implied ‘zero risk’, effectively precludes any

application of probability to an adverse event occurring

The basis for the responses to the questions posed in the qualitative matrix is contained in the

hazard sheets.

Product/hazard Sulphur dioxide in prawns

Severity Range from nasal discharge to asthma

and anaphylactic shock

Occurrence of illness No reports from prawn consumption

Increase in concentration in prawns required

to cause illness?

No

Impact of processing, handling None

Consumer terminal step? Cooking reduces concentration

Epidemiological link? None

Assessed risk Low

Product/hazard Chloramphenicol in prawns

Severity Aplastic anaemia

Occurrence of illness Rare but sometimes fatal

Chronic exposure required to cause illness? Yes – 150,000,000-735,000,000x intake

from level in prawns


Consumer terminal step? None


Assessed risk Extremely low

94

Product/hazard Nitrofurans in prawns

Severity Genotoxicity

Occurrence of illness No cases reported

Chronic exposure required to cause illness? Yes – 4,000,000-12,000,000x intake from

prawns


Consumer terminal step? No

Epidemiological link? Not in Australia

Assessed risk Very low (FZANZ risk assessment)

Product/hazard Cadmium in Prawns

Severity Disorders of kidneys, liver, intestine

Occurrence of illness Low

Chronic exposure required to cause illness? Yes


Consumer terminal step? None


Assessed risk Low

95

Appendix 1: Review Report on ‘Food Safety Risks Associated with Prawns Consumed in Australia’

Prepared jointly by:

Professor Iddya Karunasagar, Senior Fishery Industry Officer, Products, Trade and

Marketing, Fisheries and Aquaculture Department Room F524, Food and Agriculture

Organization, Viale delle Terme di Caracalla, 00153, Rome, Italy

and

Professor Alan Reilly, Chief Executive, Food Safety Authority of Ireland, Abbey Court, Lower

Abbey Street, Dublin 1, Ireland

The document ‘Food safety risks associated with prawns consumed in Australia’ has been

well prepared taking into consideration available scientific evidence on microbiological and

chemical hazards, epidemiological data from Australia and other prawn importing and

consuming regions, other national and international risk assessments. Data source and

scientific references have been indicated. The challenges involved in performing risk

assessments for chemicals have been correctly pointed out.

Detailed comments on the three TORs are given below:

1. Hazard identification: This has been based on reported cases of illness during two

decades, as well as perceived hazards causing recalls or import alerts. This section

provides good coverage for both actual hazards involved in illnesses as well as perceived

ones.

2. Hazard sheets for identified hazards:

(a) Vibrio cholerae: This is largely based on FAO/WHO risk assessment (2005) and

after this assessment was completed, there has been no new data that would warrant

reconsideration of the conclusions. Further, National Enteric Pathogen Surveillance

Scheme data has been used to identify the hazard in Australian context. Many alerts

in import testing systems arise without considering toxigenicity of isolates found and

the hazard sheet recognises this.

(b) Vibrio parahaemolyticus: The hazard sheet takes into consideration global reports of

incidence of V. parahaemolyticus in prawns and also the Australian data. We

recommend that upfront, in section 1. Hazard identification, it would be useful to

state that human illnesses are generally caused by strains that are either tdh+ or

rarely, trh+ and strains possessing these attributes constitute a very small proportion,

if at all of the natural population associated with the environment and seafood. This

point comes later in section 3.2. This would be helpful to understand the public

health risk in the right perspective, particularly in the context of natural presence of

this organism, and large number of import alerts that are triggered without testing for

toxigenicity/pathogenicity.

Response: Agreed and the text has been amended in TOR 1: Hazard Identification

(c) In Section 1.2, it will be useful to give some additional information about a large

outbreak (1,133 cases) linked to shrimp that occurred in Port Allen, Louisiana, in US

in 1978 (Morb. Mortality Weekly Rep 27: 345-346, 1978). In this situation, raw

shrimp shipped in wooden boxes were boiled, returned back to the same boxes and

transported unrefrigerated and consumed after 7-8 hr (Oliver and Kaper, 2007).

96

Response: Agreed and the text has been amended in Section 1.2 of the Hazard Sheet

for V. parahaemolyticus

Section 2, last para, it will be useful to clarify regarding sucrose negative vibrios.

The parenthesis suggests that these contain pathogenic strains. We suggest deleting

the parenthesis or changing it as ‘a category that includes V. parahaemolyticus’

because there are sucrose negative vibrios (e.g. V. harveyi) that do not cause human

infections and even among sucrose negative V. parahaemolyticus, only a very small

proportion are tdh+ and hence pathogenic. Therefore presence of sucrose negative

Vibrio count does not mean much in terms of presence of pathogenic strains.

Response: Agreed and the text has been amended in Section 2 of the Hazard Sheet


In Summary (Section 4), we think it would be useful to state that though pathogenic

strains have been detected in oysters, illnesses are rare, possibly because, when

present they are in very low numbers as indicated in last para of section 2.

Response: Agreed and the text has been amended in Section 2 of the Hazard Sheet


(d) Salmonella: The hazard sheet has been written well. In Section 3.3 Dose response,

the second sentence needs to be qualified. Low cell numbers causing outbreaks is

related to food matrix (mostly high fat foods) and there are no reports of low cell

numbers associated with seafood causing outbreaks. As noted in FAO/WHO risk

assessment for salmonella in broiler chicken and eggs (FAO/WHO, 2002), in one

outbreak related to consumption of scallop with egg yolk, 6.3 log cells resulted in

56% attack rate. Also it will be useful to point out that prawns are not considered

high fat foods.

Response: Agreed and the text has been amended in Section 3.3 of the Hazard sheet

for Salmonella

(e) Hepatitis A virus: The hazard sheet has been well written with appropriate

references.

(f) Chloramphenicol and nitrofurans: We would agree with the hazard sheet. The levels

of residues found in seafood including prawns are extremely low and pose little or

no risk to consumer health. The issue with these compounds has been that they have

been used as indicators of misuse of antibiotics that have been banned in food

producing animals.

(g) Sulphite: Agree with the hazard sheet

(h) Cadmium: Agree with the hazard sheet

3. Risk assessment of identified hazards: V. cholerae risk assessment is in line with the

FAO/WHO risk assessment and the use of Risk Ranger provides a useful semi-

quantitative output. V. parahaemolyticus assessment page 69, there is some mix-up with

Salmonella. These need to be corrected.

Response: Agreed and the typos have been amended.

Salmonella assessment is also in agreement with epidemiological data and logical. The

qualitative risk assessment for chemical hazards is quite reasonable and shows that risks

are extremely low.

97

4. Conclusions: The Draft Report adequately covers the TORs. The hazards have been

identified based on both global as well as Australian data and well referenced. We agree

that Risk Ranger is a useful tool to place the risk in a semi-quantitative context and

provide a ranking for further action by risk managers. The risk ratings obtained in this

study are realistic for the hazard:product pairing.

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