Risk factors for human anthrax outbreak in Kiruhura District, Southwestern Uganda: a population-based case control study

Abstract

Introduction: In 2018, Uganda experienced recurrent outbreaks of anthrax in both humans and livestock. We aimed to determine risk factors for human anthrax outbreak among residents of Kazo County, Kiruhura District, south-western Uganda. Methods: We conducted an unmatched case control study during March-April 2019. We defined a case as having had anthrax infection reported to be diagnosed by a healthcare worker in a resident of Kazo County between May 1st, 2018 and June 1st, 2018. A control was a resident in the nearest neighboring household who had not been diagnosed with anthrax between May 1st and June 1st and who had no symptoms suggestive of anthrax in May 2018. We obtained participants' sociodemographic, clinical and exposure characteristic using a structured questionnaire. We performed logistic regression to identify risk factors for human anthrax. Results: We recruited 101 participants (28 cases and 73 controls) with median age of 34 (IQR; 26-47) years; most (61.4%) were female. The overall attack rate was 1.9%, while the most common clinical manifestations were ulcers (96.4%) and fever (96.4%). The risk factors for contracting human anthrax were: slaughtering of anthrax infected animals (aOR=5.74; 95%CI: 1.39-23.8), consuming of anthrax infected meat (aOR=6.4; 95%CI: 1.53- 6.7) and being male (aOR=12.8; 95%CI: 3.31-49.1). Conclusion: the point source outbreak in humans was predominantly of the cutaneous form as a result of contact with anthrax infected meat. We recommend community sensitization on safe disposal of carcasses, avoiding slaughtering/handling carcasses, and carrying out routine livestock vaccinations against anthrax in Uganda to avert similar outbreaks in future.