Impact of population based indoor residual spraying in combination with mass drug administration on malaria incidence and test positivity in a high transmission setting in north eastern Uganda

Background: Mass drug administration (MDA) and indoor residual spraying (IRS) are potent malaria burden reduction tools. The impact of combining MDA and IRS is not well documented. We evaluated the impact of MDA+IRS compared to IRS alone at a high transmission site in Eastern Uganda. Methods: : A quasi-experimental study was implemented in Toroma and Kapujan subcounties in north eastern Uganda. Both subcounties received four rounds of IRS using primiphos-methyl (Acttellic SC300) six to eight months apart from December 2016 to December 2018. Eligible residents of Kapujan simultaneously received MDA using dihydroartemesinin-piperaquine (DHA-PQ). Health facility data was used to monitor malaria case incidence rate and test positivity rates. Results: : In the MDA+IRS arm, malaria incidence dropped by 83% (IRR: 0·17 (0·16– 0·18); p<0·001) in children under 5 year and by 78% (IRR: 0·22 (0·22– 0·23); p<0·001) in persons aged ≥ 5 years from the pre-intervention to the intervention period. In the IRS arm malaria incidence dropped by 47% (IRR: 0·53 (0·51, 0·56); p<0·001) in children under 5 years and by 71% 0·29 (0·28, 0·30); p<0·001) in persons aged ≥5 years. A drastic drop occurred immediately after the intervention after which cases slowly increased in both arms. Malaria test positivity rate (TPR) dropped at a rate of 21 (p=0·003) percentage points per 1000 persons in the MDA+IRS arm compared to the IRS arm. There was a mean decrease of 60 (p-value, 0·040) malaria cases among children under five years and a mean decrease in TPR of 16·16 (p-value, 0·001) in the MDA+IRS arm compared to IRS arm. Interpretation: MDA significantly reduced malaria burden among children <5 years however the duration of this impact needs to be further investigated. Funding: Pilgrim Africa, Government of Uganda Ministry of Health