Impact of indoor residual spraying on malaria incidence in Ugandan prisons: an interrupted time series analysis.

Abstract

Background: Indoor residual spraying (IRS) is an effective 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 had been performed. The study assessed the general malaria incidence trends for 5 years and determined the impact of IRS on malaria incidence in the main prison facilities in Uganda.

Methods: This was a cross-sectional study which employed interrupted time series analysis to determine the effect of IRS programme on malaria incidence in prisons located in two different regions of Uganda. The malaria incidence trends of two prison facilities per region (in similar settings) were compared, one being an IRS intervention facility and the other being a comparison facility (did not receive an IRS) over 5 years (2018-2022) in the central and northern regions of Uganda.

Results: A total of 208 monthly malaria reports from all selected facilities (4) were reviewed. The peak malaria incidence rate 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 population per month for the central and northern regions, respectively) than among the comparison facilities (177.0 and 170.6 cases per 1000 population 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: 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.