Impact of Indoor Residual Spraying on Malaria Burden in the main Prison Facilities in Uganda

Background Indoor residual spraying (IRS) is a powerful intervention for reducing mosquito vector density and malaria transmission. Uganda Prison Services (UPS) routinely implements IRS for malaria control in main prison facilities; however, no assessment of its impact has been performed. We assessed the general malaria incidence trends for a period of five years and determined the impact of IRS on malaria incidence in the main prison facilities in Uganda. Methods This study had a cross-sectional design. We compared the malaria incidence trends in two prison facilities, one being an IRS intervention facility and the other being a comparison facility that did not receive an IRS in similar settings over a period of five years (2018–2022) in the central and northern regions of Uganda. Malaria incidence rate trends were generated, and interrupted time series analysis was conducted to assess the impact of IRS on the malaria incidence rate. Results A total of 208 monthly malaria reports from all selected facilities were reviewed. The peak malaria incidence was recorded from September to December across the years in both regions. The lowest incidence rate was recorded from January to March. The average monthly malaria incidence rate for the study period was much lower among the intervention facilities (7.1 and 13.3 cases per 1000 people per month for the central and northern regions, respectively) than among the comparison facilities (177.0 and 170.6 cases per 1000 people per month for the central and northern regions, respectively). The post-IRS intervention periods had lower malaria incidence rates than the pre-IRS periods across the intervention facilities in both regions. The IRS intervention had a statistically significant effect on reducing the malaria incidence rate in the intervention facility located in the northern region (slope: P = 0.001, CI = [21.9, 67.7]). Conclusion In general, indoor residual spraying reduced the malaria incidence rate among the intervention facilities in both regions, but a significant impact was recorded in the northern region, which is a region with higher malaria transmission rates than the central region. In situations of limited resources, IRS implementation should prioritize prisons located in high malaria transmission areas to achieve significant impacts.