A New Serotype of Vibrio Parahaemolyticus Is Becoming the Main Epidemic Strain in China

Background: During surveillance, we found a new type of Vibrio parahaemolyticus that agglutinated with O4 serum but not with K serum, and its recA housekeeping gene was affected by a large insertion. We named this strain “O4:KUT-recAin”. Methods: We analyzed clinical data from acute diarrhea patients. By serum agglutination tests and sequence analyses, we identified a new type of V. parahaemolyticus strain. Through the establishment of a rabbit diarrhea model, we confirmed the pathogenicity of this strain. Findings: O4:KUT-recAin strain possessed a new type of K antigen, a 25,043 bp large fragment encoding 20 proteins inserted in the housekeeping gene recA. Retrospective analysis found that only one O4:KUT-recAin strain was detected in 2014; then, the proportion increased rapidly and reached 17·8% in 2016 and 31·1% in 2017, making O4:KUT-recAin the second dominant serotype following O3:K6. O4:KUT-recAin strains exhibited increased acid resistance and could reproduce in medium at pH= 4·9, while most of the O3:K6 strains could not grow at this pH. O4:KUT-recAin could cause diarrhea and small intestinal tissue lesions in infant rabbits, but its diarrhea and mortality rates were slightly lower than those of O3:K6. Based on diarrhea patients, most clinical symptoms and laboratory results were comparable in the two groups. Interpretation: O4:KUT-recAin had enhanced acid resistance, was capable of causing infectious diarrhea in both rabbits and humans, and became widespread during a short period of time in China. Therefore, it is necessary to raise global awareness and perform surveillance and molecular epidemiological studies to avoid further spread of O4:KUT-recAin. Funding Statement: This work was supported by the grants from the National Key Programs for Infectious Diseases of China (2017ZX10103008), the National Nature Science Foundation of China (81802067) and Sanming Project of Medicine in Shenzhen (SZSM201811071). Declaration of Interests: We declare no competing interests. Ethics Approval Statement: The study protocol was approved by the ethics committees of the First Affiliated Hospital, College of Medicine, Zhejiang University, and all participants provided written informed consent.