Factors Associated with Malaria in Regions Implementing Case Based Surveillance in Mainland Tanzania, August 2021 to May 2022

Introduction: A malaria case-based surveillance system (mCBS) was established in Kilimanjaro, Arusha, and Manyara regions in Tanzania following reports of very low parasite prevalence. The system aims to eliminate malaria by 2030, but had not been analyzed since its start. Our study used data from August 2021 to May 2022 to identify factors associated with malaria among contacts of local cases Methods: This was a cross-sectional study that analyzed mCBS data collected between August 2021 and May 2022. The dataset included index cases and contacts information obtained through proactive and reactive case detection methods (pro-ACD and re-ACD respectively). Multivariate logistic regression was used to identify factors associated with malaria among contact cases. Statistical significance was tested at a 95% confidence interval and p-value ≤ 0.05 Results: From August 2021 to May 2022, 949 malaria cases were reported, with 63.8% being over 16 years old, median age 20 years. Most cases were local-introduced (96.5%), males accounting for 54.8%. Arusha region reported most cases (53%). Among 642 tested contacts, 51% were female, and only 3.7% tested positive. Factors associated with lower malaria positivity included, household size ≥ six members (aOR = 0.11, 95% CI = 0.02 – 0.62), being afebrile past three days (aOR = 0.03, 95% CI = 0.01 – 0.14), having no history of contact with individuals on malaria treatment within past 28 days (aOR = 0.01, 95% CI= 0.004 – 0.04), as well as having no history of travel to malaria-endemic areas within past 28 days (aOR= 0.24, 95% CI = 0.06 – 0.92) Conclusion: A history of contact with a household member treated for malaria or had travelled to an endemic area in past 28 days as well as a family size with fewer than three members are risk factors for malaria in regions implementing case-based surveillance in Tanzania.