Integrated Transmission Assessment Survey (iTAS) in Nigeria

The pre iTAS sample size is about 3,000 individuals ages 10 and older, and 1,500 individuals ages 5 to 9. The iTAS sample size is 15,000 children ages 5 to 9. 

Mass administration of medicine (MAM) with ivermectin (Mectizan) is the recommended strategy for elimination of onchocerciasis (OV) and, combined with albendazole, for lymphatic filariasis (LF). As areas begin reaching sufficient numbers of effective rounds of MAM, decisions on when to stop need to be made. The30-cluster, random-sample transmission assessment survey (TAS) is routinely used by LF programs to guide MAMstopping decisions. In 2016, the World Health Organization (WHO) published criteria for MAMstopping decisions for OV. This can also be used to identify areas of persistent transmission for further intervention. The present study used a modified TAS (iTAS) to inform both LF and OV stopping decisions in 4 formerly-endemic local government areas (LGA) in Nigeria that had completed 16-17 years of MAM for OV and 5-6 years of MAM for LF. In each LGA, 3,000 children ages 5-9 were targeted for sampling via cluster random sampling of 30 schools. All were tested for LF antigenemia with the filariasis test strip (FTS) and for antibodies against OV and LF via the Ov16/Wb123 Biplex rapid diagnostic test (RDT). Dried blood spots were also taken. All 4 LGAs had FTS prevalence below the critical threshold for passing LF TAS (i.e., stopping MAM).One LGA, Bade, passed the threshold for stopping OV treatment with 0% positive Ov16 results. The other 3 LGAs, Karim Lamido, Gashaka, and Bekwarra, did not pass with 0.03%, 1.7% and 3.6% Ov16 positivity respectively. In Gashaka and Bekwarra, positive results clustered in a few schools. In Gashaka, Ov16 prevalence ranged from 0-23%, with 11 schools having 0 positives. In Bekwarra, Ov16 prevalence ranged from 0-13% with 5 schools having 0 positives. Investigation of these ‘hotspots’ of ongoing OV transmission identified after many years of MAM is needed. This new iTAS appears to be successful in facilitating stopping decisions for both programs and identifying areas in need of further intervention.