Foodborne Illness Outbreak Investigation Amongst Party Guests in Highfield Suburb, Harare City, Zimbabwe, 2020: A Retrospective Cohort Study

Background: On November 2, 2020, 5 patients presented at Highfield Polyclinic with fever, diarrhoea, abdominal pain, vomiting and some with dehydration after attending the same party on October 31, 2020. We aimed to determine the factors associated with this outbreak and identify a possible etiological agent. Methods: We conducted a retrospective cohort study to investigate a foodborne illness amongst party guests in Highfield Suburb, Harare City, 2020. Pretested questionnaires were administered to participants drawn from the guest list along with environmental and outbreak preparedness and response checklists. We reviewed medical records of cases who presented at the health facility. No food samples were available for testing. Fifteen stool and four water samples were collected and analyzed at the Beatrice Road Infectious Diseases Hospital (BRIDH) and Government Analyst Laboratories. Sixty-three out of 80 guests were interviewed. Attack rates were calculated for each food exposure, and relative risks (RRs) were calculated by comparing attack rates among exposed and unexposed groups for specific food items using Epi Info 7.2.4.0. Results: Forty guests who consumed food at the party became ill. The median age was 16 years (Q1 =10; Q3 =32). All cases reported abdominal cramps, while 36 (90 %) experienced watery diarrhoea and fever. The median incubation period was 12 hours (Q1 = 6; Q3 = 30). No pathogens were isolated from the stool and water samples. The independent risk factors for contracting foodborne illness were eating coleslaw adjusted RR= 7.4 (95% CI: 1.1– 50.0; p-value = 0.04) and eating cold macaroni adjusted RR=4.1 (95% CI: 1.1- 14.7; p-value = 0.03). The outbreak was detected over 48 hours after the initial cases. Harare City health facility was well prepared with essential supplies, including oral rehydration solutions, intravenous fluids, antibiotics, and personal protective equipment. However, the food for the event was prepared without refrigeration, transported at room temperature, and handled by untrained, uncertified food handlers. Conclusion: The outbreak was identified as a common point-source foodborne outbreak, with coleslaw and cold macaroni as possible vehicles of transmission. The course of illness largely fit that of a toxin-producing pathogen. The outbreak investigation identified gaps in food safety practices. While there was a delay in outbreak detection, Harare City health facilities were adequately stocked with essential supplies and adhered to standard treatment protocols. These findings underscore the need for enhanced food safety education and stricter regulations for food handlers, as well as improved outbreak surveillance and rapid response systems.