A Protracted Malaria Outbreak in Upper Muzarabani, Centenary District, Zimbabwe, 2023

Introduction: From week 1 to week 29 of 2023, David Nelson Clinic in Upper Muzarabani reported a persistent surge in malaria cases surpassing weekly thresholds, a shift from the known geospatial burden of malaria in Centenary District. We carried out an outbreak investigation to determine drivers of the protracted malaria outbreak. Methods: We conducted a 1:1 unmatched case control study of 156 respondents (78 cases and 78 controls). We defined a case as a resident of Upper Muzarabani who presented with symptoms consistent with malaria and tested malaria positive on malaria rapid diagnostic test between week 1 and week 29 of 2023. We described the outbreak in time, place and person using proportions, analysed entomological and rainfall patterns to determine vector and rainfall trends. We conducted bivariate and backward stepwise multivariate logistic regression analysis to determine human host related factors. Results: A total of 2763 case patients were recorded, giving an overall attack rate of 13.2% (2763/20 886 at risk population) with a case fatality of 0.14% (4 deaths/2763 cases). An 8.5% (525mm to 574mm) increase in rainfall was recorded between 2018 and 2022. 26.6% sampled mosquitoes expressed genetic pyrethroid insecticide resistance. Staying near a water body (aOR=4.69; 95% CI 1.99-11.07), engaging in late night (aOR=3.86; 95% C.I 1.64-9.06) and early morning outdoor activities (aOR=4.18; 95% C.I 1.61-10.83) were independent risk factors for contracting malaria. Availability of long-lasting insecticide-treated nets in all household sleeping areas (aOR=0.2; 95%CI 0.09-0.49) and wearing protective clothing when outdoors during peak mosquito biting times (aOR=0.30; 95% CI 0.10-0.86) were independent protective factors against contracting malaria. Conclusion: Engagement in outdoor activities during peak vector biting times, vector adaptation and optimal vector breeding conditions were key factors associated with the protracted malaria outbreak. We recommended establishment of a district One Health committee to spearhead insecticide resistance surveillance and preparedness for climate-related health threats.