District Mapping Onchocerciasis and Lymphatic Filariasis in Kenya: Assessing Sampling Strategies for Onchocerciasis Elimination Mapping (OEM)

As onchocerciasis programs in Africa shift from a paradigm of control to one of elimination, there is a need to determine whether transmission is ongoing in previously-untreated areas. To do so, there is a need to develop a mapping strategy that is rigorous enough to detect low levels of ongoing transmission while also using resources efficiently. A multi-country operational research study was conducted comparing sampling in purposively-selected communities, random sampling in randomly-selected communities, and random sampling in the schools in which the majority of children from the randomly-selected villages attended. In Kenya, random sampling was also used in purposively-selected communities. Six sub-countries in Kenya were included in the study: Bonchari, Bureti, Hamisi, Kasipul, Lunga Lunga, and Mt Elgon. All of these sub-counties are located in Western Kenya near the Ugandan border, with the exception of Lunga Lunga, which is located in coastal Kenya on the Tanzanian border. Seroprevalence by Ov16 rapid diagnostic test (RDT) was very low in all sub-counties. In randomly-selected villages, prevalence was 0.1% in Bureti, 0.2% in Hamisi, and 0.1% in Mt. Elgon. No positive RDT results were found in Bonchari, Kasipul, or Lunga Lunga. The only positive results found in purposively-selected communities were in Bonchari (0.1%). Interpretation of results in this context is still ongoing.