Malaria infection clustered into small residential areas in lowlands of southern Ethiopia

Malaria is a complex disease and its distribution is not random in endemic areas, and hence areas with low malaria transmission require fine spatial sampling and careful follow-up to identify the hot spots for effective resource utilization to control malaria. The present study is aimed to assess malaria infection in both humans and mosquitoes in a small residential lowland area of southern Ethiopia from July to December 2016. A repeated cross-sectional household survey was conducted in Kolla-Shara Kebele (village) to describe the distribution of malaria and infectious mosquitoes. For the parasitological surveys, a total of 90 households were randomly selected from five sub-villages in equal proportion. About a quarter of the total households included for the surveys were randomly selected for entomological surveys. A P-value of <0.05 was used as a cut-off point for statistical significance. More than a third (35.1%, 46 of 131) febrile cases were microscopically confirmed malaria positive. Above half (58.7%, 27 of 46) of those positive cases were due to P. falciparum and the rest (41.3%, 19 of 46) were due to P. vivax. This study identified two of the five sub-villages as independent clusters with higher risk of malaria infection. Four times higher relative risk (RR) of malaria infection was documented in Abullo sub-village compared to the others (RR = 3.87; P = 0.002). Most of the falciparum malaria cases were aggregated in these sub-villages. About six infectious bites of An. arabiensis per person was recorded during the survey. The infectious bite per person was 17.0 in Abullo and 10.6 in Erze clusters where higher human infections were detected. It is clearly indicated that a smaller portion of the population carry higher malaria cases and infectious bites. Malaria interventions targeting such areas could be effective in the context of malaria elimination strategy in Ethiopia, which consider district as a planning and implementing unit. Future research would preferably be designed to perform long duration of follow-up to identify the appropriate period for interventions and more participants with more heterogeneous villages and districts.