Investigation and etiological detection of a foodborne disease outbreak caused by Vibrio parahaemolyticus in Nantong City

ObjectiveTo systematically investigate a foodborne disease outbreak caused by Vibrio parahaemolyticus （V. parahaemolyticus） in Nantong City through epidemiological investigation， laboratory testing， whole-genome sequencing， and antimicrobial susceptibility testing， with the aim of providing scientific evidence and practical experience for the prevention and control of similar incidents in the future.MethodsSamples were collected from suspected contaminated food， patient rectal swabs， food handler rectal swabs， and environmental surface swabs from food preparation areas. Conventional pathogen isolation and identification were performed， followed by virulence gene detection， WGS， and antimicrobial susceptibility analysis of the isolates.ResultsA total of 9 V. parahaemolyticus strains were isolated， including 8 from patient rectal swabs and 1 from a water sink in the preparation area. All 8 patient isolates carried the tlh and tdh genes， whereas the environmental isolate carried only tlh. None of the isolates harbored the trh gene. cgSNP analysis showed high homology， with differences between case isolates ranging from 2 to 18. Multilocus sequence typing （MLST） identified all isolates as sequence type 3 （ST3），and the annotated resistance genes were highly consistent with the drug resistance phenotypes. Drug susceptibility testing was conducted using 22 antibiotics， and the results showed that among the 8 case isolates， 7 were resistant to cefazolin， 6 to ampicillin， and 5 were intermediate to cefuroxime.ConclusionThis outbreak was attributed to the ST3 clone of V. parahaemolyticus. Detection of virulence genes and WGS provided critical genomic insights for source tracing and contamination path determination. Clinically， treatment should prioritize drugs with demonstrated efficacy， while cefazolin， ampicillin， and cefuroxime should be avoided to ensure timely symptom relief and prevent disease progression.