Outbreak investigation of food poisoning in a university, Maha Sarakham Province, Thailand, 4–10 June 2025

Abstract

Background: Foodborne illness results from consuming food or water contaminated with various pathogens, typically presenting with gastrointestinal symptoms. On June 6, 2025, the Situation Awareness Team (SAT) of the Maha Sarakham Provincial Public Health Office was notified by Maha Sarakham Hospital of a cluster of foodborne illness cases during a freshman orientation activity at a university in Maha Sarakham Province. An investigation team was formed to confirm the outbreak and diagnosis, describe the distribution of illness, identify risk factors, and propose control and prevention measures.

Methods: A descriptive and analytical study using a 1:1 case-control design was conducted among participants attending the activity during June 4–6, 2025. Data were collected using questionnaires. Univariable analysis was performed using chi-square/Fisher's exact test to calculate odds ratios (OR), 95% confidence intervals (CI), and p-values (p < 0.1). Multiple logistic regression was used to calculate adjusted odds ratios (aOR), 95%CI, and p-values (p < 0.05). Environmental assessments were conducted at the university and two food vendors, and laboratory investigations included samples from patients, food handlers, and the environment.

Results: A total of 591 cases were identified, most of whom were female (72%) and first-year students (85.45%), with a median age of 18 years. Common symptoms included abdominal pain (84.4%), diarrhea (78.7%), watery stool (69.7%), fever (53.8%), and nausea (43.7%). The mean incubation period was 12 hours, and the epidemic curve suggested an intermittent common-source outbreak. Multivariable analysis showed significant associations between illness and stir-fried chicken with basil and bamboo shoots with fried egg (aOR 1.95), stir-fried chicken in curry paste with bamboo shoots and rolled omelet (aOR 4.12), and stir-fried pork with yellow chili peppers and fried egg (aOR 1.71). Sanitation deficiencies were identified at both food vendors, including inadequately cooked eggs, reuse of gloves, lack of food handler health screening, and prolonged storage of food at room temperature. Salmonella serogroup D was isolated from patients' stool samples, coliform bacteria were detected on kitchen utensils and food handlers' hands at both vendors, and Aeromonas hydrophila and Plesiomonas shigelloides were isolated from ice samples.

Conclusions: This outbreak was caused by Salmonella serogroup D, with an intermittent common-source pattern linked to food from two vendors; the definitive source of contamination remains unknown. Similar sanitation deficiencies were found at both vendors. No new cases were identified following implementation of control measures.