Epidemiological Assessment of Eight Rounds of Mass Drug Administration for Lymphatic Filariasis in India: Implications for Monitoring and Evaluation

Abstract

BackgroundMonitoring and evaluation guidelines of the programme to eliminate lymphatic filariasis require impact assessments in at least one sentinel and one spot-check site in each implementation unit (IU). Transmission assessment surveys (TAS) that assess antigenaemia (Ag) in children in IUs that have completed at least five rounds of mass drug administration (MDA) each with >65% coverage and with microfilaria (Mf) levels <1% in the monitored sites form the basis for stopping the MDA. Despite its rigour, this multi-step process is likely to miss sites with transmission potential (‘hotspots’) and its statistical assumptions for sampling and threshold levels for decision-making have not been validated. We addressed these issues in a large-scale epidemiological study in two primary health centres in Thanjavur district, India, endemic for bancroftian filariasis that had undergone eight rounds of MDA.Methodology/Principal FindingsThe prevalence and intensity of Mf (per 60 µl blood) were 0.2% and 0.004 respectively in the survey that covered >70% of 50,363 population. The corresponding values for Ag were 2.3% and 17.3 Ag-units respectively. Ag-prevalence ranged from 0.7 to 0.9%, in children (2–10 years) and 2.7 to 3.0% in adults. Although the Mf-levels in the survey and the sentinel/spot check sites were <1% and Ag-level was <2% in children, we identified 7 “residual” (Mf-prevalence ≥1%, irrespective of Ag-status in children) and 17 “transmission” (at least one Ag-positive child born during the MDA period) hotspots. Antigenaemic persons were clustered both at household and site levels. We identified an Ag-prevalence of ∼1% in children (equivalent to 0.4% community Mf-prevalence) as a possible threshold value for stopping MDA.Conclusions/SignificanceExistence of ‘hotspots’ and spatial clustering of infections in the study area indicate the need for developing good surveillance strategies for detecting ‘hotspots’, adopting evidence-based sampling strategies and evaluation unit size for TAS.

Determinants of transmission hotspots and filarial infection in households after eight rounds of mass drug administration in India

“…With such high levels of compliance, one would expect interruption of transmission in both areas, as has been reported elsewhere [28,29]. However, evidence of ongoing transmission in the hotspots [15,16] suggests that responses regarding compliance in previous rounds of MDA in the questionnaire survey could have been subject to recall bias over a period of 8 years, resulting in overestimation of compliance rates.…”

“…The communities surveyed in this study are in Thanjavur district, which recorded an MDA coverage of 56–92% and MDA compliance of 34–53% in the period 2001–2010 . The reported Mf prevalence in the district is 0.16% in 2001 and 0.09% by 2008.…”

“…The overall prevalences of Mf and Ag were <0.4% and 2.7% after eight rounds of MDA . Of the 33 sites, 12 were hotspots (Mf prevalence >1% or had Ag positive children in the age group of 2–8 years) and the remaining 21 were non‐hotspots . It should be noted that all hotspots were semi‐urban and most non‐hotspots were rural.…”

“…The PHC has 33 sites (18 villages and 15 wards) covering a population of 19 147 living in 5910 households and had undergone eight annual rounds of MDA from 2000 to 2008 (4 with DEC alone and 4 with DEC+albendazole) with a reported coverage of 88–92% in different sites. The overall prevalences of Mf and Ag were <0.4% and 2.7% after eight rounds of MDA . Of the 33 sites, 12 were hotspots (Mf prevalence >1% or had Ag positive children in the age group of 2–8 years) and the remaining 21 were non‐hotspots .…”

Fifteen years of programme implementation for the elimination of Lymphatic Filariasis in Ghana: Impact of MDA on immunoparasitological indicators

“…However, LF is a focal disease and the 50-km grid method [6], the WHO LF mapping protocol [4], and TAS [5] have the potential to miss LF endemic communities [21,22]. It is therefore important to develop new LF mapping protocols that could be used to reevaluate districts previously considered nonendemic in LF endemic countries.…”