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

Decision rules for confirmatory mapping surveys.

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

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

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

Schematic showing the study designs in Ethiopia and Tanzania.

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

Results of a confirmatory mapping tool for <i>Lymphatic filariasis</i> endemicity classification in areas where transmission was uncertain in Ethiopia

<div><p>Background</p><p>The goal of the global <i>lymphatic filariasis</i> (LF) program is to eliminate the disease as a public health problem by the year 2020. The WHO mapping protocol that is used to identify endemic areas in need of mass drug administration (MDA) uses convenience-based sampling. This rapid mapping has allowed the global program to dramatically scale up treatment, but as the program approaches its elimination goal, it is important to ensure that all endemic areas have been identified and have received MDA. In low transmission settings, the WHO mapping protocol for LF mapping has several limitations. To correctly identify the LF endemicity of woredas, a new confirmatory mapping tool was developed to test older school children for circulating filarial antigen (CFA) in settings where it is uncertain. Ethiopia is the first country to implement this new tool. In this paper, we present the Ethiopian experience of implementing the new confirmatory mapping tool and discuss the implications of the results for the LF program in Ethiopia and globally.</p><p>Methods</p><p>Confirmatory LF mapping was conducted in 1,191 schools in 45 woredas, the implementation unit in Ethiopia, in the regions of Tigray, Amhara, Oromia, SNNP, Afar and Harari, where the results of previous mapping for LF using the current WHO protocol indicated that LF endemicity was uncertain. Within each woreda schools were selected using either cluster or systematic sampling. From selected schools, a total of 18,254 children were tested for circulating filarial antigen (CFA) using the immuno-chromatographic test (ICT).</p><p>Results</p><p>Of the 18,254 children in 45 woredas who participated in the survey, 28 (0.16%) in 9 woredas tested CFA positive. According to the confirmatory mapping threshold, which is ≥2% CFA in children 9–14 years of age, only 3 woredas out of the total 45 had more CFA positive results than the threshold and thus were confirmed to be endemic; the remaining 42 woredas were declared non-endemic. These results drastically decreased the estimated total population living in LF-endemic woredas in Ethiopia and in need of MDA by 49.1%, from 11,580,010 to 5,893,309.</p><p>Conclusion</p><p>This study demonstrated that the new confirmatory mapping tool for LF can benefit national LF programs by generating information that not only can confirm where LF is endemic, but also can save time and resources by preventing MDA where there is no evidence of ongoing LF transmission.</p></div

Recent map showing revised LF-endemic woredas in Ethiopia, 2015.

<p>67 woredas already confirmed to be endemic are shown in brown. Three woredas confirmed to be endemic with this confirmatory mapping are shown in stripe line. Non-Endemic woredas as per the confirmatory mapping shown in green are 42 and Non-endemic woredas as per the previous mapping are shown in yellow. Unmapped 58 woredas are shown in greyish_yellow. <a href="http://www.gadm.org/" target="_blank">www.gadm.org/</a> is the source of the administrative boundaries.</p

List of nine woredas with CFA positive children.

<p>List of nine woredas with CFA positive children.</p

Map showing LF-endemicity status of woredas in Ethiopia.

<p>Endemic woredas are shown in Brown. Uncertain 45 woredas with <1% CFA+ shown in Orange. Non-Endemic woredas shown in Yellow. Unmapped 58 woredas shown in greyish_yellow color. <a href="http://www.gadm.org/" target="_blank">www.gadm.org/</a> is the source of the administrative boundaries.</p