Outbreak Investigation of a Foodborne Illness in Village Bachal Soomro, District Tharparkar, Sindh, Pakistan (December 2020): Retrospective Cohort Study

Abstract

Background On December 3, 2020, district health authorities reported 15 suspected cases of gastroenteritis, including 4 deaths, from Village Bachal Soomro after a mourning ceremony. Objective Field Epidemiology and Laboratory Training Program (FELTP) fellows investigated the suspected outbreak, with the objective to determine the magnitude of the outbreak and to evaluate associated risk factors. Methods A retrospective cohort study was conducted on December 3, 2020, at Village Bachal Soomro. The complete cohort was traced back, and a pretested structured questionnaire was adopted to obtain demographic, clinical, and risk factor information. A case was defined as “any individual who attended the mourning ceremony at Village Bachal Soomro on December 3, 2020, and presented with any of the following symptoms: diarrhea, abdominal pain/cramps, and drowsiness.” Descriptive analysis followed by multiple logistic regression was performed. Different blood, stool, oropharyngeal swab, drinking water, and milk samples were sent for microbiological and chemical investigation. Results Of 61 participants, 32 (52%) were males and the median age was 23 years (range 1-70 years). The overall attack rate was 72%, while the most affected age group was 10-19 years, with an attack rate of 85%. The majority of cases presented with diarrhea (47/61, 77%), followed by abdominal pain (44/61, 72%), vomiting (43/61, 70%), body ache (29/61, 48%), drowsiness (10/61, 16%), and fever (4/61, 7%). Among all food items, dessert had the highest food-specific attack rate of 90%. Among all risk factors, consumption of dessert (adjusted odds ratio [aOR] 61.3, 95% CI 6.1-613.1), water (aOR 23.9, 95% CI 2.0-276.7), and buffalo milk (aOR 7.9, 95% CI 1.22-51.8) were found to be significantly associated with the attack. Distribution of cases showed a common point source that was probably due to a single pathogen source. Conclusions Dessert was prepared 10-12 hours prior to meal intake, so the outbreak was probably caused by dessert prepared with contaminated milk and water, with enterotoxins of Staphylococcus aureus. Community awareness of personal hygiene, proper storage/preservation of food items, and provision of safe drinking water are suggested.