Surveillance – an introduction Preben Aavitsland.

Surveillance – an introduction

Preben Aavitsland

Surveillance

n. Close observation, especially of a suspected spy or criminal

ORIGIN C19: from Fr., from sur- 'over' + veiller 'watch'

 Source: The Concise Oxford Dictionary. Ed.

Pearsall J. Oxford University Press, 2001.

Surveillance – original use

Close observation of individuals suspected of incubating serious infectious diseases in order to detect initial symptoms of disease in time to institute treatment and isolation.

Until 1950s

Origins of surveillance

• 1839-79 William Farr– collected, analysed, interpreted vital statistics,

– plotted rise and fall of epidemics of infectious diseases

– disseminated information in weekly, quarterly, and annual reports, medical journals, public press

• 1880-90s In Europe and USA doctors must reported communicable diseases

• 1923 Sanepid system started in the Soviet Union

• 1925 National surveillance system in USA

Towards a new concept

Alexander Langmuir (1910 – 1993)

• Continued watchfulness over the distribution and trends of incidence through the systematic collection, consolidation and evaluation of morbidity and mortality reports and other relevant data together with the timely and regular dissemination to those who need to know

• General practice of “epidemiologic intelligence”

• In 1963

In the words of WHO

World Health Assembly in 1968:

• Systematic collection of pertinent data

• Orderly consolidation and evaluation of these data

• Prompt dissemination of the results to those who need to know

"Information for action"

Surveillance

Systematic ongoing collection, collation and analysis of data and the timely dissemination of information to those who need to know so that action can be taken.

Source: A Dictionary of Epidemiology. 4th edition. Ed. Last J. Oxford University Press, 2001

Surveillance

• World Health Assembly 2005 with the new International Health Regulations

• ”The systematic ongoing collection, collation and analysis of data for public health purposes and the timely dissemination of public health information for assessment and public health response as necessary.”

Surveillance

Surveillance is the ongoing systematic collection, collation, analysis and

interpretation of data; and the dissemination of information (to those

who need to know) in order that action may be taken

Information for action!

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Rationale for surveillance

The disease

• Severity

• Frequency

• Communicability

• International obligations

• Costs

• Preventability

Society

• Public and mass media interest

• Will to prevent

• Availability of data

Priority setting – which diseases?

• Incidence / prevalence• Severity• Epidemic potential• Socio-economic impact• Cost• Preventability • Public concern and news-worthiness• Feasibility

Possible objectives of surveillance

• Monitor trends (by time, place, person)– towards a control objective

– as programme performance

– as intervention evaluation

• Detect outbreaks

• Estimate future disease impact

• Collect cases for further studies

….in order to [action]

Actions resulting form surveillance

…in order to:

• implement control measures (rapid response)

• prioritise public health resources

• design and plan public health programmes

• plan and conduct research

• …

SMART objectives

Specific

Measurable

Acceptable and Action-oriented

Realistic

Time-related

Examples

Vague...• To estimate the frequency of hepatitis C• To detect outbreaks of measles

Specific and action-oriented• To measure the incidence of hepatitis C in

France in order to allow planning of specific health care needs for the coming 20 years

• To detect early time and place clustering of measles cases in order to ensure timely control of outbreaks

Ex: To monitor progress towards polio eradication by monitoring the incidence of poliomyelitis where wild

poliovirus is isolated in children under 14 years

0

50

100

150

200

250

80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96

National immunisation days

Cases of poliomyelitis where wild poliovirus was isolated in children in a rural district, 1980-1996

Ex: To measure the incidence of AIDS to predict future trends and facilitate health service planning

0

100

200

300

400

500

600

700

90 91 92 93 94 95 96 97 98 99 0 1 2 3 4

Cases of AIDS in a city district, 1990-2004

Ex: To monitor trends in the proportion of resistant gonorrhoea in order to guide empiric antibiotic therapy

0

10

20

30

1975 1980 1985 1990 1995 2000

0

100

200

300

400

% No./100 000

PPNG proportion

Incidence of gonorrhoea and proportion with PPNG in Norway 1975-2003

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Event and population under surveillance

Population and time• Everyone in the

country or defined part of the country

• Patients in hospitals• Employees in a factory• All children in the

winter months• …

Event• Disease• Syndrome

– Accute flaccid paralysis– Influenza-like illness– Diarrhoea

• Infection• Public health issue

– Antimicrobial resistance• Environment

– Vector population– Water quality

• …

Exposed

Clinical specimen

Symptoms

Pos. specimen

Infected

Seek medical attention

Diagnosis

Exposed

Clinical specimen

Symptoms

Pos. specimen

Infected

Seek medical attention

DiagnosisLab-confirmed disease

Severe disease

Mild diseaseAsymptomatic infection

Syndrome

What is better: A system based on clinical cases or a sysem based on

laboratory confirmed cases?

Indicators

• A calculated measure that indicates the changes you want to monitor

• Decide one or more indicators that sums up the surveillance results

• For example– Number of cases– Number of cases per 100 000 population per year

(incidence rate)– Percentage children under 1 year among meales

cases– Median age at first sexual intercourse– Percentage unemployed among 50 year olds

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Case definition

Includes• (Time, place, person)• Clinical featuresand /or• Laboratory resultsand/or• Epidemiological features

Should be• Clear, simple• Field tested• Stable and valid

Ex. Meningococcal disease is any person with symptoms of meningitis or septicaemia and Neisseria meningitidis detected from blood or cerebrospinal fluid by culture or PCR.

Sensitivity versus specificity

Sensitivity versus specificity

Sens

Spec

Sensitivity and predicitive value

Sensitivity

• = reported true cases total true cases

• = proportion of true cases detected

Positive predictive value

• = reported true cases total reported cases

• = proportion of reported cases are true cases

The tiered case definition

Confirmed

Probable

Possible

Features of different definitions

• “Confirmed” (specific) case-definition– low sensitivity - includes few cases

– high specificity - includes mostly true cases

– few false positive cases

• “Possible” (sensitive) case-definition– high sensitivity - includes almost all cases

– low specificity - includes also many non-cases

– many false positive cases

Exposed

Clinical specimen

Symptoms

Pos. specimen

Infected

Seek medical attention

DiagnosisConfirmed case

Probable case

Do you want a mainly sensitive or a mainly specific case definition for

measles?

Case definitions and reporting criteria

Case definition

Measles

Confirmednnn nnn nnnn nn

Probablenn nnn nnn nnnn

Possiblennnnnn nn n nnn

Reporting criteria

”Measles”

OutputMeasles

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Data sources

• Hospitals• Ambulatory clinics• General practitioners• Clinics for sexually

transmitted diseases• Laboratories• Selected sites -

sentinel surveillance system

• Schools• Work places• Existing data collection

systems (death certificates, sick leave system etc)

• Public sector • Private sector• Non-governmental

organisations

Exposed

Clinical specimen

Symptoms

Pos. specimen

Infected

Seek medical attention

DiagnosisLaboratories

Schools, work places

General practitioners

Hospitals

Issues with differen data sources

• Cost

• Representativeness

• Acceptability

• Data quality

• Timeliness

• Confidentiality

Data collection instrument

• Data form or no specified format?

• Open or closed questions?

• Data requirements specified?

Reporting form

Reporting form

Database

Database

Copy

Interpretation

Information versus acceptability

Info

Accept

Aggregation of data

• Individual data– Identified – name, personal id number

– Non-identified – but possible to trace back

– Anonymous – impossible to trace back

• Aggregated data– Numbers

– Tabulated numbers – by sex, age group etc

Reporting (data transfer)

Data transfer method

• Paper by mail

• Telephone

• Telefax

• E-mail

• Internet

• Protected net

Data transfer frequency

• For every case

• Daily

• Weekly

• Monthly

• Zero reporting

Active versus passive surveillance

Passive

• Wait for reporters to report

• May have low sensitivity

• Used in most surveillance systems

Active

• Reach out to potential reporters regularly

• More sensitive

• More resource-demanding

• Used for special diseases or periods

Quality checking

• Reporting regularity

• Report quality

• Follow up procedures

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Data analysis and interpretation

From data to indicators to interpretation• Data validation (completeness + validity)• Descriptive analysis: time, place, person• Generating and testing hypotheses related to

time, place, person– Advanced analyses

• Time series analysis• Cluster analysis

• Interpretation– Using supporting information

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Information and feedback

• Contents– Surveillance information– Interpretations– Recommendations– Other information

• Format– Text– Tables– Figures

• Target audience– Public– Professionals– Policy makers

• Medium– Newsletter

• Paper• Fax• E-mail• Internet

– Web-tool

• Frequency– Immediately– Daily– Weekly– Monthly

Web tool – example from Norway

Feedback has its own value

• Shows respect for those who report

• Increases adherence to system

• Forces you to analyse and interpret

What is the feedback from the surveillance system in your country?

The surveillance loop

Event

Action

Data

Information

Health care system

Surveillance centre

Reporting

Feedback, recommendations

An

alysis, in

terpretation

Information for action!

• Surveillance is not for archives!

• Action– implement control measures

• rapid response

– prioritise public health resources• policy change?

– design and plan public health programmes

If there is no action..

..it isn’t surveillance

Ethical issues: right or wrong

• Build trust between public health practitioners and the society

• Issues:– Self-interest or desire to benefit society?– Potential benefits and harms. For whom?– Maximise benefits. Minimise harms– Involvement of community representatives– Rights of people

• Confidentiality – share only with those who have permission from patient or legal right to know

– Respect for people

Legal issues

• Surveillance systems should have a legal foundation that specifies– How to collect information– How to use information

• Not for other purposes– How to safeguard and store information– How to allow individuals to see and correct information

• Main principles– Collect only what you need– Choose the lowest level of identification needed– Analyse and publish rapidly

Functions

Core functions

• Detection

• Reporting

• Investigation & confirmation

• Analysis & interpretation

• Action/response

Support functions

• Training

• Supervision

• Resources

• Standards/guidelines

Who does what?

Resources for system operation

• Funding sources• Personell time• Other costs

– Training– Mail– Forms– Computers– ...

Your most important assets

• A good network of motivated people

• Clear case definition and reporting mechanism

• Efficient communication system

• Basic but sound epidemiology

• Laboratory support

• Good feedback and rapid response

Rapid reporting Analysis Action

Identify two major weaknessesin the surveillance system

for communicable diseasesin your country

Evaluation of surveillance systems

• Systematic investigation of the merit of the surveillance system in order to increase its usefulness and efficiency

Importance of evaluatingsurveillance systems

• Quality– Often neglected

– Basis for improvements

• Obligation– Does the system deliver?

– Credibility of public health service

• Learning process– ”Do not create one until you have evaluated one”

General framework for evaluation

• A. Engagement of stakeholders

• B. Evaluation objective

• C. System description

• D. System performance

• E. Conclusions and recommendations

• F. Communication

C. System description

• 1 Public health rationale (why?)

• 2 Objectives (what?)

• 3 Operations (how?)

• 4 Resources (how much?)

Extreme learning value!!!!

D. System performance

Does it work?System attributes• Simplicity• Flexibility• Data quality• Acceptability• Sensitivity• Positive predictive value• Representativeness• Timeliness• Stability

Is it useful?

Use of information• Users

• Actions taken

Link to objectives

Timeliness

Occurence of event

Recognition of event

(diagnosis)

Reporting of event

Action taken

E. Conclusions and recommendations

• Proper rationale?

• Attributes – Balance of attributes and costs

• Fulfilling objectives?

• Recommendations– Continue

– Revise: specify

– Stop

Surveillance – a big challenge

• Crude

• Inaccurate

• Incomplete

• Cumbersome

• Complex