Analysis of dominant serotypes of Vibrio parahaemolyticus in diarrhea patients from 2020 to 2023 in Huzhou, China

BACKGROUND: V. parahaemolyticus with serotype O3:K6 was first isolated in 1996 and subsequently caused outbreaks of gastroenteritis worldwide. Serotype O10:K4 was detected in 2020 and quickly became dominant in many places of China and Thailand. V. parahaemolyticus with new serotypes and indistinguishable antigens have constantly emerged in Huzhou in recent years. METHODS: The V. parahaemolyticus strains were isolated from fecal samples of diarrhea patients treated at the First People's Hospital of Huzhou. The serotypes and multipoint sequence typing (MLST) of these isolates were analyzed. RESULTS: A total of 325 specimens were identified as positive for V. parahaemolyticus from 9451 fecal samples during 2020 to 2023. The overall detection rate was 3.41% and was relatively high from May to September each year. V. parahaemolyticus infection was found in all age groups tested, with the 16-40-year age group having the highest detection rate (48.0%), followed by the 41-60-year age group (31.38%). The clinical features of the V. parahaemolyticus-associated patients were mainly fever, vomiting, diarrhea, nausea and abdominal pain. Among all isolates, 261 isolates were fully serotyped, 8 isolates were O undetermined and 62 isolates were K undetermined. The dominant serotypes were O10:K4 (n = 152), and O3:K6 (n = 71). From 2020 to 2023, 114 isolates of V. parahaemolyticus with serotypes O3:K6, O4:KUT and O10:K4 were randomly selected for whole genome sequencing. Serotypes O3: K6 and O10: K4 both belonged to ST3, while serotype O4: KUT was divided into 3 STs: ST3, ST332 and ST2516/265. Core-genome MLST (cgMLST) clustering analysis showed that O3:K6 and O10:K4 were basically clustered together. O4: KUT was clearly divided into three clusters. CONCLUSIONS: This study confirms the sustained prevalence of V. parahaemolyticus O10:K4 and the emergence of different ST types of O4:KUT in Huzhou area, which may lead to food poisoning incidents.