The rationale and cost-effectiveness of a confirmatory mapping tool for lymphatic filariasis: Examples from Ethiopia and Tanzania

<div><p>Endemicity mapping is required to determining whether a district requires mass drug administration (MDA). Current guidelines for mapping LF require that two sites be selected per district and within each site a convenience sample of 100 adults be tested for antigenemia or microfilaremia. One or more confirmed positive tests in either site is interpreted as an indicator of potential transmission, prompting MDA at the district-level. While this mapping strategy has worked well in high-prevalence settings, imperfect diagnostics and the transmission potential of a single positive adult have raised concerns about the strategy’s use in low-prevalence settings. In response to these limitations, a statistically rigorous confirmatory mapping strategy was designed as a complement to the current strategy when LF endemicity is uncertain. Under the new strategy, schools are selected by either systematic or cluster sampling, depending on population size, and within each selected school, children 9–14 years are sampled systematically. All selected children are tested and the number of positive results is compared against a critical value to determine, with known probabilities of error, whether the average prevalence of LF infection is likely below a threshold of 2%. This confirmatory mapping strategy was applied to 45 districts in Ethiopia and 10 in Tanzania, where initial mapping results were considered uncertain. In 42 Ethiopian districts, and all 10 of the Tanzanian districts, the number of antigenemic children was below the critical cutoff, suggesting that these districts do not require MDA. Only three Ethiopian districts exceeded the critical cutoff of positive results. Whereas the current World Health Organization guidelines would have recommended MDA in all 55 districts, the present results suggest that only three of these districts requires MDA. By avoiding unnecessary MDA in 52 districts, the confirmatory mapping strategy is estimated to have saved a total of $9,293,219.</p></div

Summary of confirmatory mapping tool results by district from Ethiopia and Tanzania, 2015.

<p>Summary of confirmatory mapping tool results by district from Ethiopia and Tanzania, 2015.</p

Decision rules for confirmatory mapping surveys.

<p>Decision rules for confirmatory mapping surveys.</p

Schematic showing the study designs in Ethiopia and Tanzania.

<p>Schematic showing the study designs in Ethiopia and Tanzania.</p

Cost savings resulting from confirmatory mapping in Ethiopia and Tanzania, calculated by comparing the costs of the mapping surveys with the averted costs for districts that passed and did not required MDA treatment.

<p>Cost savings resulting from confirmatory mapping in Ethiopia and Tanzania, calculated by comparing the costs of the mapping surveys with the averted costs for districts that passed and did not required MDA treatment.</p

Results from the standard WHO mapping protocol (adults >15 years in two villages per district) from same districts as the confirmatory mapping tool implementation in Tanzania in 2015.

<p>Results from the standard WHO mapping protocol (adults >15 years in two villages per district) from same districts as the confirmatory mapping tool implementation in Tanzania in 2015.</p

Spatial distribution and antigen positivity rates of schools selected for TAS surveys on Pemba and Unguja islands in Zanzibar, United Republic of Tanzania.

<p>Spatial distribution and antigen positivity rates of schools selected for TAS surveys on Pemba and Unguja islands in Zanzibar, United Republic of Tanzania.</p

Map of The Gambia showing the location and microfilaria (MF rates in 15 villages surveyed in 1975 and 1976 (adapted from Reference #20) in areas of low transmission (Blue) where MF rates were less than 10% (Upper River and Western Divisions) and high transmission (Red) where MF rates where greater than 18% (Central River Division).

<p>Map of The Gambia showing the location and microfilaria (MF rates in 15 villages surveyed in 1975 and 1976 (adapted from Reference #20) in areas of low transmission (Blue) where MF rates were less than 10% (Upper River and Western Divisions) and high transmission (Red) where MF rates where greater than 18% (Central River Division).</p

Map showing the locations of 1315 communities surveyed in Ethiopia during the mapping project in 2013.

<p>Eighty-nine communities in which one or more persons out of 100 individuals tested were found to be positive for circulating filarial antigen (CFA) are shown in red. Communities where no positive individuals were identified after testing approximately 100 adults are marked in blue.</p

Map of The Gambia showing the location of 60 schools surveyed during the Transmission Assessment Surveys (TAS) carried out in 2013 and revealing no circulating filarial antigen (CFA) positive individuals in all schools indicated by the white dots.

<p>Map of The Gambia showing the location of 60 schools surveyed during the Transmission Assessment Surveys (TAS) carried out in 2013 and revealing no circulating filarial antigen (CFA) positive individuals in all schools indicated by the white dots.</p