Outbreak investigation of food poisoning in a school, Khao Cha Mao District, Rayong Province, Thailand, 11–14 March 2019

Abstract

Background: On 9 March 2019, Division of Epidemiology received a notification from Rayong Provincial Public Health Office that found a cluster of food poisoning in school, Khao Cha Mao District. Thirty six patients, of whom 5 patients were treated in Khao Cha Mao Hospital, with the symptoms including vomiting, nausea and abdominal pain. The joint Investigation team investigated during March 11th–14th, 2019 to determine epidemiological characteristics of the outbreak, to find the source of outbreak and to recommend control measures.
Methods: A descriptive and retrospective cohort study was conducted. We interviewed patients using structured questionnaire and performed active case finding using the designated case definition. In addition, environmental study and food preparation processing were explored by walk through survey and interview food handlers and teachers. We collected rectal swab and vomitus samples of cases and food handlers, and environmental specimens such as swab of utensils. Then, sent the specimens for enteropathogenic bacteria isolation and virus at Department of Medical Sciences. Univariable and Multivariable analysis were performed and presented with Relative risk (RR), Adjusted odds ratio (Adjusted OR) and 95% Confidence interval (CI).
Results: There were 98 cases met case definition, attack rate was 47.12%. The common clinical presentation was vomiting (90.82%), followed by nausea (78.57%) and abdominal pain (72.45%). The Epidemic curve demonstrated common source. The suspected foods were shrimp paste fried rice (Adjusted OR 2.46, 95% CI 0.73–8.24), winter melon soup (Adjusted OR 2.04, 95% CI 0.74–5.65), spicy fried eggs with salad (Adjusted OR 1.85, 95% CI 0.86– 3.98), sour soup (Adjusted OR 1.78, 95% CI 0.78–4.05). Rectal swabs among food handlers and environmental samples found Norovirus, B. cereus and Aeromonas spp.
Conclusions and discussions: The event is an outbreak of food poisoning in the school at Khao Cha Mao District, Rayong Province, caused by B. cereus. The suspected source was contaminated water, poor food hygiene and inadequate processing. The disease surveillance after the outbreak showed no additional patients. Further, the treated water should be used for cooking or cleaning utensils and outbreak disease investigation skill for teachers in charge of school health should be improved.