Objective

On 1 December 2020, the Department of Disease Control of Thailand was notified of a cluster of food poisoning cases among participants at a church festival in Mae Ai district, Chiang Mai province. We conducted an outbreak investigation to confirm diagnosis, describe the epidemiological characteristics of the outbreak, identify possible sources of the outbreak, and provide appropriate control measures.

Methods

We reviewed medical records of the food poisoning cases from the health care centers. Active case finding was conducted among participants who had consumed food and water at the festival. An environmental survey was done in the village where the festival was held. A case-control study was conducted to identify the source of the outbreak. Samples for laboratory analysis included rectal swabs and fresh stool specimens from the cases and food handlers, surface swabs of cooking equipment, food, water and ice samples.

Results

Among 436 participants surveyed, 368 (84.4%) cases of food poisoning were identified. The most common clinical manifestation was abdominal pain (89.7%), followed by watery diarrhea (45.7%), nausea (43.5%), vomiting (38.9%), fever (18.5%) and bloody diarrhea (4.6%). None died in this outbreak. The case-control study showed that mixed spicy seafood salad served in the festival was significantly associated with the disease by both univariable and multivariable analyses. However, the causative agent could not be identified. The environmental investigation suggested this seafood might have been undercooked.

Conclusion

Clinical manifestations of the cases, incubation period, and the suspected seafood salad suggested seafood-related food poisoning. Grimontia hollisae (G.hollisae), the organism causing illness similar to Vibrio parahaemolyticus and commonly undetectable in the laboratory with routine testing, might be the pathogen that caused this outbreak. G.hollisae should be in differential diagnosis and identified in seafood-associated outbreaks.