Efficacy and cost-effectiveness of outdoor residual spraying with α-cypermethrin, pirimiphos-methyl, and deltamethrin against sand flies: A cluster randomised controlled field trial in Uganda.

Introduction: Visceral leishmaniasis is a significant public health challenge in East Africa. Achieving the WHO 2030 requires novel control strategies. In this study, we evaluated the efficacy and cost-effectiveness of three insecticide formulations for outdoor residual insecticide spraying (ORS) in Uganda. Methods A clustered randomised controlled field trial was conducted in five clusters. Three clusters were randomly allocated to receive ORS with either α-cypermethrin, pirimiphos-methyl, or deltamethrin, while the two clusters served as untreated controls. The primary outcome was the change in sandfly counts per trap night, measured using CDC light and sticky traps before and after the intervention. Results After spraying the insecticides in the intervention villages, the sandfly population declined by 62%, 60%, and 49% with α-cypermethrin, pirimiphos-methyl, and deltamethrin, respectively. Sandfly captures increased by 353% in the control villages in the same period. Using a negative binomial regression with village-clustered standard errors, α-cypermethrin reduced sandfly counts by 93% compared to the change in control villages (IRR = 0.07, 95% CI 0.05–0.11, p < 0.001). Pirimiphos-methyl and deltamethrin reduced counts by 92% (IRR = 0.08, 95% CI 0.05–0.12, p < 0.001) and 89% (IRR = 0.11, 95% CI 0.07–0.19, p < 0.001), respectively. A cost-effectiveness analysis showed that α-cypermethrin was the most cost-effective option, followed by deltamethrin and lastly pirimiphos-methyl, with annual cost per village of $382, $390 and $408, respectively. Conclusion Our findings provide evidence-based guidance for vector control programs. The high efficacy and superior cost-effectiveness of α-cypermethrin make it a strong candidate for inclusion in integrated vector management strategies targeting outdoor sandfly populations in this region.