Malaria positivity rate trend analysis from 2013-2021 at water resources development project of Wonji Sugar Estate Oromia, Ethiopia

Abstract Background: Evidence on the trends of the proportion of malaria infections detected by routine passive case detection at health facilities is important for public health decision making especially in areas moving towards elimination. This study assessed nine years of trends on clinical malaria infections detected at health facility and its associated climate factors, in the water resource development set up of Wonji sugar estate, Oromia, Ethiopia. Methods: From January, 2013 to December 2021, retrospective data were collected from malaria suspected patient recording logbook at Wonji sugar factory’s primary hospital. Monthly average mereological data were obtained from the estate meteorological station. Results: Over the last nine years, 34,388 cases were legible for analysis with complete data. Of these, 11.75% (4,039/34,388) were positive for clinical malaria. Plasmodium vivaxtest positivity was the highest proportion (8.2%, n=2,820) followed by Plasmodium falciparum (3.48%, n=1,197) and mixed infections (P. falciparumand P. vivax, 0.06%, n=21). The odds of being positive for malaria was highest in males (AOR = 1.46; 95%CI: 1.36-1.52; P<0.001) compared to females, in older individuals of above 15 years old (AOR=4.55, 95%CI=4.01-5.17, P<0.001) followed by school-age children (5–15 years old) (AOR=2.16; 95%CI: 1.88–2.49, P<0.001). There was no significant variation in the proportion of malaria-positive cases in the dry and wet seasons (P=0.059). Malaria test positivity rates were associated with average monthly rainfall (AdjIRR=1.00; 95%CI=1.00-1.001, P<0.001) while negatively associated with average monthly minim temperature (adjIRR=0.94; 95%CI=0.94–0.95; P<0.001) and average monthly relative humidity (adjIRR=0.99, 95%CI=0.99- 1.00, P=0.023). Conclusion: There was year-round malaria transmission, adults especially males and school children frequently tested malaria positive. Hence, alternative vector management tools like larval source management have to be deployed besides ITNs and IRS in such water development areas to achieve the malaria elimination goals.