post-mda surveillance ( including xeno-monitoring) krishnamoorthy k. vector control research centre...
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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