Factors associated with a malaria outbreak at Tongogara refugee camp in Chipinge District, Zimbabwe, 2021: a case-control study

Background Malaria is a leading cause of morbidity and mortality among forcibly displaced populations, including refugees, approximately two-thirds of whom reside in malaria endemic regions. Data from the rapid disease notification system (RDNS) reports for Manicaland Province in Zimbabwe showed that despite implementation of malaria control initiatives, there was an increase in number of malaria cases above action thresholds at Tongogara refugee camp in Chipinge district during weeks 12-14 of 2021. An investigation that described the outbreak by person, place and time was conducted. Malaria emergency preparedness, response, and appropriateness of case management were assessed. The factors associated with contracting malaria were determined to enable the formulation of appropriate interventions, establish control, and prevent future malaria outbreaks among this vulnerable population. Methods A 1:1 unmatched case-control study involving 80 cases and 80 controls was conducted using interviewer-administered questionnaires at household level. Data was entered into Epi Data version 3.1 and quantitative analysis was done using Epi Info (TM) version 7.2.2.6 to generate medians, proportions, odds ratios and their 95% confidence intervals. Results Malaria cases were distributed throughout the 10 residential sections within Tongogara refugee camp, the majority being from section 7, 28 (35%). Despite constituting 11% of the total population, Mozambican nationals accounted for 36 (45%) cases. Males constituted 47 (59%) among cases which was comparable to controls 43 (54%), p = 0.524. The median age for cases was 15 years [Interquartile range (IQR), 9-26] comparable to controls, which was 17 years (IQR, 10-30) (p = 0.755). Several natural and man-made potential vector breeding sites were observed around the camp. Risk factors associated with contracting malaria were engaging in outdoor activities at night [AOR = 2.74 (95% CI 1.04-7.22), wearing clothes that do not cover the whole body during outdoor activities [AOR 4.26 (95% CI, 1.43-12.68)], while residing in a refugee housing unit reduced the risk of contracting malaria [AOR = 0.18 (CI, 0.06-0.55)]. Conclusions The malaria outbreak at Tongogara refugee camp reemphasizes the role of behavioural factors in malaria transmission. Intensified health education to address human behaviours that expose residents to malaria, habitat modification, and larviciding to eliminate mosquito breeding sites were recommended.