Objective To understand the epidemiological characteristics of a foodborne disease outbreak caused by Vibrio parahaemolyticus after a wedding banquet in Huzhou, Zhejiang province, in 2024, analyze the etiological characteristics of the isolated strains, and provide evidence for the prevention and control of similar epidemics.

Methods The cause of the outbreak was investigated by using field epidemiology, food hygiene, and laboratory testing methods. Whole-genome sequencing was conducted on bacterial isolates, followed by phylogenetic tree construction based on single nucleotide polymorphisms (SNP) to perform microbial source tracking of the pathogen.

Results Approximate 510 people attended the banquet, in whom 21 became ill, with an attack rate of 4.12%. The main symptoms of the cases were vomiting, abdominal pain, and diarrhea. The epidemic curve indicated a point-source exposure, and the average incubation period was 12.30 hours. V. parahaemolyticus was detected in 11 stool samples from the cases and 2 leftover food samples (steamed abalone with vermicelli and babylonia areolata). The tlh and tdh genes were detected in all the isolates from the cases, belonging to serotype O4:Kut. The tlh gene was detected in the isolates from the two food samples, belonging to serotype O5:Kut. All the 13 strains were resistant to cefazolin. Whole-genome sequencing analysis revealed that approximate 57 730 SNP variant loci were detected in the isolates from both case samples and food samples, indicating they were from different clones.

Conclusion The pathogen of this outbreak was V. parahaemolyticus, and the infection might occurred in dinner on June 1^st. The suspected food was steamed abalone with vermicelli. Whole-genome sequencing analysis suggested that the predominant strain of V. parahaemolyticus might change in spread from food to humans.