Post-MDA surveillance ( including xeno -monitoring)

Post-MDA surveillance (including xeno-monitoring)

Krishnamoorthy K.Vector Control Research Centre Pondicherry

India

• Development of an appropriate and feasible surveillance strategy to monitor the post-MDA epidemiological situation is necessary to:

a) declare the areas/intervention units are free from LF transmission or

b) take steps to prevent resurgence of infection, if any.

• Antigenaemia prevalence has been recommended to monitor post MDA situation. However, the change in this parameter during the post MDA period (five years) is not known to understand the usefulness of this indicator and also to decide on the frequency of post MDA survey.

Rationale

Study area

Villages PopulationMf prevalence

Pre MDA Post 3 rounds

Post 6 rounds

% reduction (pre-post 6)

Kallakulathur 1203 7.61 0.00 0.00 100

Keelidayalam 2609 4.27 2.95 0.41 90

Sendiampakkam 517 11.36 4.35 0.00 100

Sitheni 2083 10.95 4.67 0.47 96

Total 6412 8.10 3.80 0.34 96

Intervention = Mass annual single dose DEC + albendazoleSix rounds – supervised administration (2001-2007)Coverage = above 70%Post 6 rounds of MDA = <1% mfAg prevalence (3-6 years) = 0/93Stopped MDA in 2008

1-5 6-10 11-15 16-19 20-24 25-29 30-34 35-39 40-45 46-49 50-55 56-60 >600

50

100

150

200

250

300

350Age specific population in the study villages

KallakulathurKeelidayalamSendiampakkamSitheni

Age class in years

Num

ber o

f ind

ivid

uals

Objectives

• To understand the post-MDA changes in antigenaemia prevalence in children (6-10 years)

• To relate the post-MDA changes in antigenaemia prevalence in children with the antigenaemia prevalence in adult groups (16-45 years)

• To evaluate the value of xenomonitoring as a tool for post-MDA surveillance

• To determine the required duration of post-MDA surveillance period

Evaluation Unit

Evaluation Unit - four villages

Village Households Female Male TotalKallakulathur 127 449 419 868Keelidayalam 359 1042 1031 2073Sendiampakkam 101 364 352 716Sitheni 277 1039 903 1942Grand Total 864 2894 2705 5599

2001 2002 2003 2004 2005 2006 2007

Coverage 71.2255090280446

73.0037313432834

75.9741531231643

66.312893081761

0 61.8973862536301

71.0940499040307

5.00

15.00

25.00

35.00

45.00

55.00

65.00

75.00

Coverage (DoT) of MDA

Year

Perc

enta

ge

2-10 11-20 21-30 31-40 41-50 51-60 >60

Baseline 3.73831775700935 7.0063694267516 9.21052631578947 8.86075949367089 11.4754098360656 9.80392156862745 8.16326530612245

Post 6 0 0 0 2.35294117647059 0 0 0

1.00

3.00

5.00

7.00

9.00

11.00

13.00

Mf prevalence

Per

cent

age

Overall 7.76 %n=580

Overall 0.05%n=585

Indicators and tools1. Antigenemia (mass) survey in :

• Diagnostic tool – ICT• Target age class

o 6-10 years (children)

o 16-45 years (adults)

2. Entomological survey:

• 5000 vector mosquitoes

• Gravid traps

• Dissection to assess the vector infection

These surveys were repeated after two years. The first survey was done in 2011 and the second in 2013

12.8

%

57.8 %

29.4 %

Figure 1.Distribution of study population by age (n= 5599)

6-10 yrs16-45 yrsOthers

2013Villages 6-10 years 16-45 years Total

SampleAg +ve % Sample

Ag +ve % Sample

Ag +ve %

Kallakulathur 84 0 0.00 355 5 1.41 439 5 1.14

Keelidayalam 182 0 0.00 1281 12 0.94 1463 12 0.82

Sendiampakkam 81 1 1.23 414 4 0.97 495 5 1.01

Sitheni 205 3 1.46 1361 22 1.62 1566 25 1.60

Total 552 4 0.72 3411 43 1.76 3963 47 1.19

2011Villages 6-10 years 16-45 years Total

SampleAg +ve % Sample

Ag +ve % Sample

Ag +ve %

Kallakulathur 61 0 0.0 299 3 1.0 360 3 0.8Keelidayalam 175 2 1.1 672 26 3.9 847 28 3.3Sendiampakkam 196 2 1.0 754 18 2.4 950 20 2.1Sitheni 69 1 1.5 263 5 1.9 332 6 1.8Total 501 5 1.0 1989 52 2.6 2490 57 2.3

Year 6-10 years 6-10 years

Population Sample Coverage (%) Population Sample Coverage (%)

2011 (post MDA 3) 550 502 91.3 2728 1918 70.3

2013 (Post MDA 5) 735 552 75.10 3411 2432 71.30

Coverage for ICT survey

Ag prevalence during post MDA

Post 6 rounds of MDA Post MDA 3 (2011) Post MSA 5 (2013)

6-10 years 1.9 1 0.7

16-45 years 15.4 2.6 1.3

1

3

5

7

9

11

13

15

17

6-10 years 16-45 years

Ag p

reva

lenc

e (%

)

6-10 16-450.00.51.01.52.02.53.03.54.04.55.0

1.00

2.62

0.72

1.76

Ag prevalence with 95% C.I. by target age in 2011 and 2013

2011 2013

Age class (years)

Prev

alen

ce (%

)

2011

2013

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.50.0

0.4

0.8

1.2

1.6

Relationship between Ag prevalence in 6-10 years and 16-45 years age classes

2011Linear (2011)2013Linear (2013)

Ag prevalence in 16- 45 years age class

Ag p

reva

lenc

e in

6-1

0 ye

ars

age

clas

s

TAS exercise (6-7 years)

Year Population Sample Coverage (%)

Ag +ve

2011 262 144 54.9 0

2013 234 155 65.4 0

Ag survey

Longitudinal (cohort) folllow-up

Total = 1053Positive in 2011 = 23Loss in 2013 = 19 (82.6%)Negative in 2011 = 1030Gain in 2013 = 15 (1.46%)

Entomological survey – (2011)

Village TrapsVector (C.q)

Trap density

Infection Intensity Infectivity

Collected Dissected Positive

Kalla Kulathur 90 1219 1219 0 13.54 0.00 0.0 0

Sithani 94 1920 1920 5 20.43 0.26 1.4 0

Keezh Edayalam 107 1195 1195 0 11.17 0.00 0.0 0

Sendiampakkam 107 1208 1208 2 11.29 0.17 2.0 0

Total 398 5542 5542 7 13.92 0.13 1.6 0

Entomological survey – (2013)

Village Population

No. collections

No. traps

No. collected

Density range per trap

Per trap density

No. dissected

No. infected

No. infective

Sithani 2083 12 59 1328 1-69 22.51 1328 0 0

Keelidayalam 2609 13 101 1306 1-32 12.93 1306 0 0

Kallakulathur 1203 7 54 1381 1-54 25.57 1381 0 0

Sendiampakkam 517 12 93 1267 1-64 13.62 1267 0 0

Total 6412 44 307 5282 1-69 17.21 5282 0 0

Period of survey 3 months

04-12-2012 26-02-2013

• Absence of recent transmission in two consecutive post-MDA surveys indicate that 1% Mf prevalence was safe to discontinue MDA.

• Prevalence of antigenemia prevalence among children (6-10 years) is less than 1% during post MDA period.

• Post-MDA Ag-prevalence between children and adult age class is not related, and therefore adult age class cannot be targeted for evaluation. There was reduction in antigenemia prevalence in both children (28%) and adult age classes (33%). The relative change in Ag prevalence between the age classes was also not significant.

• Loss of infection was about 83%.

• Xenomonitoring after two years of stopping MDA did not show evidence for vector infection implying absence of potential mf carriers in the study community.

Conclusion