Association between entomological indices and malaria test positivity rates in Western Kenya: implications for surveillance

Abstract

Abstract The relationship between malaria entomological indices and epidemiological outcomes remains poorly understood at local scales in western Kenya, limiting evidence-based surveillance strategies. This study evaluated associations between malaria test positivity rates and vector densities, human biting rates, and entomological inoculation rates (EIR) in a high-transmission setting. The study was conducted in five villages within Teso South sub-County, Busia County, Kenya, from March to June 2021. Village-level entomological indices including vector densities, human biting rates (HBR), and entomological inoculation rates (EIR) were calculated for Anopheles funestus and An. gambiae s.l . Concurrent malaria test positivity rates were obtained from outpatient department registers in the health facilities serving the five villages (n = 2377 cases). The relationship between entomological indices and malaria test positivity was analyzed using multilevel logistic regression models, accounting for individual- and village-level factors. During this period 1950 female anopheline mosquitoes, predominantly An. gambiae s.l (89.0%) and An. funestus (11.0%) were collected. Malaria test positivity rates varied significantly across villages (range: 23.6%-68.7%). Multilevel analysis revealed significant associations between malaria test positivity and both anopheline mean density (OR 1.11, 95% CI 1.08–1.15, p < 0.0001) and HBR (OR 1.35, 95% CI 1.17–1.57, p < 0.0001). However, an association between EIR and malaria test positivity was not observed (OR 1.04, 95% CI 0.96–1.13, p = 0.316). These findings suggest that one solution to address foci with higher malaria cases is to target transmission through vector control based on health facility surveillance. This information could be valuable for national malaria control programs in optimizing surveillance strategies and evaluating intervention effectiveness.