Epidemiological and Whole-Genome Sequencing Analysis of a Gastroenteritis Outbreak Caused by a New Emerging Serotype of Vibrio parahaemolyticus in China

Vibrio parahaemolyticus is an important foodborne pathogen with diverse serotypes. In May 2021, we investigated a gastroenteritis outbreak that occurred in China, caused by V. parahaemolyticus O10:K4 infection. Based on the epidemiological curve, this outbreak was identified as a homologous exposure event. A case-control study demonstrated that emperor crab with mashed garlic (odds ratio [OR] = 4.60, p = 0.030; 95% confidence interval [95% CI]: 1.11-19.14), goose liver geoduck (OR = 4.50, p = 0.029; 95% CI: 1.12-18.13), shrimp (OR = 4.89, p = 0.021; 95% CI: 1.22-19.65), and sea cucumber (OR = 7.36, p = 0.005; 95% CI: 1.68-32.26) were the potential sources of the food poisoning. V. parahaemolyticus isolates from 18 laboratory-confirmed cases were all serotyped O10:K4, and determined to be sequence type ST3 via multilocus sequence typing. Pulsed field gel electrophoresis and whole-genome sequencing analysis revealed the identical pattern and 0-2 single nucleotide variation among these isolates. tdh was positive in all isolates, while trh and Orf8 were absent. Seven essential base positions in toxRS for pandemic clone identification were identical between the O10:K4 and O3:K6 pandemic clones. Phylogenetic analysis with 45 additional genomes of 13 different serotypes showed the closest genetic relationship between O10:K4 and O1: KUT. O10:K4 was thought to evolve from the O3:K6 pandemic clone. The new serovariant of O3:K6 poses a challenge for the prevention and control of V. parahaemolyticus disease outbreaks, or even epidemics, in the future.