Objective To ascertain the causes of a food poisoning incident and provide references for the prevention of similar incidents in the future.

Methods Case investigation was conducted through field epidemiological investigation methods， and suspicious meals and foods were searched by the analytical epidemiological method. A food hygiene investigation was conducted in the establishment involved and samples of suspicious food， processing steps， and cases were collected for laboratory testing.

Results A total of 91 individuals meeting the case definition were identified， resulting in an attack rate of 14.97% （91/608）. The main clinical manifestations included abdominal pain （97.80%）， diarrhea （84.62%）， nausea （62.64%）， vomiting （72.53%）， fever （12.09%）， and increased white blood cells （90.11%）. The peak incidence occurred from 16：00 to 18：00 on June 15. The epidemic curve showed a point-source exposure pattern， with an incubation period of 1 h minimum and 10 h maximum， and an average of 5 h. Analytical epidemiological studies indicated that lunch on June 15 was the suspicious meal （χ²=38.78， P<0.001）， and those who consumed cold-dressed tofu with preserved eggs had a significantly higher risk of falling ill compared to non-consumers （χ²=105.21， P<0.001）. Laboratory testing results revealed Vibrio parahaemolyticus detected in 1 employee’s anal swab and 18 cases’ anal swabs. Staphylococcus aureus was detected in 1 food ingredient and 1 case’s anal swab. The remaining samples tested negative.

Conclusion The cause of this food poisoning incident is Vibrio parahaemolyticus. The cause is the canteen’s supply of cold-dressed tofu with preserved eggs beyond its permissible business scope， potentially leading to cross-contamination during food processing. Regulatory authorities should strengthen routine law enforcement inspections and monitoring. Food service establishments should strengthen food safety awareness， standardize operational procedures in strict accordance with relevant national laws and regulations and food safety standards， and strive to reduce the occurrence of foodborne disease incidents at their source.