Research – Vital Surveillances: Phylogenetic Analysis of Serogroup O5 Vibrio cholerae that Caused Successive Cholera Outbreaks — Guangdong Province, China, 2020–2021

China CDC

Food Illness

  • Abstract

    IntroductionGastroenteritis caused by non-O1/non-O139 Vibrio cholerae exhibited an increasing trend in recent years in China. Whole genome sequence (WGS) data could play an important role both in the identification of the outbreaks and in the determination of the serogroup. Here, we present the employment of WGS data in the investigation of two outbreaks caused by non-O1/non-O139 V. cholerae in Guangdong, China, 2020–2021.

    MethodsWe obtained the whole genome sequence of 66 V. cholerae strains isolated in two outbreaks with next generation sequencing technology. We retrieved the publicly available WGS data of non-O1/non-O139 V. cholerae from public database. We used a pipeline integrated in China Pathogen Identification Net (PIN) to complete the phylogenetic analysis.

    ResultsTwo outbreaks caused by non-O1/non-O139 V. cholerae were identified using WGS data. These V. cholerae strains were determined as serogroup O5. Type 3 and 6 secretion systems were detected in these serogroup O5 strains. These serogroup O5 strains belonged to sequence type (ST) 88.

    ConclusionsOur analysis indicated the risk of non-O1/non-O139 V. cholerae of leading to outbreaks of diarrheal diseases. The application of genomic data played important role in the identification of the serogroup of non-O1/non-O139 V. cholerae in the lack of antiserum, which gave an example of the application of genome data in disease surveillance and public health emergency response.

  • Vibrio cholerae consists of more than 200 serogroups. The classification of serogroups is based on the O antigen of the lipopolysaccharide (LPS) (1). The classical method of serogroup determination is based on the immune agglutination reaction between the O antigen and the corresponding specific antiserum. The molecular mechanisms of different serogroups are based on the variation in structure of O-antigen polysaccharide (O-PS) coding sequence (2). Therefore, the phenotype of O-antigen is correlated with the molecular type of O-PS coding sequence. Till now, only serogroup O1 and O139 V. cholerae caused cholera epidemics and pandemics (3). V. cholerae does not belong to serogroup O1 and O139 and are designated as “non-O1/non-O139” V. cholerae. Usually, these non-O1/non-O139 V. cholerae only cause sporadic infections and seldomly cause outbreaks (4). Several kinds of toxins, such as a heat-stable toxin, cholera toxin, and other enterotoxins, have been detected in the non-O1/non-O139 V. cholerae that caused an outbreak. Except for the toxins, secretion systems, for example type 3 secretion system (T3SS) and type 6 secretion system, have been detected in some V. cholerae strains that caused cholera outbreaks (5).

    In China, toxigenic serogroup O1 and O139 V. cholerae strains were rarely isolated after 2010 (6). In contrast, sporadic cholera cases even small scale of outbreaks caused by non-O1/non-O139 V. cholerae were reported from time to time (4). Here we report successive cholera outbreaks caused by non-toxin-producing serogroup O5 V. cholerae in 2020 and 2021 in Guangdong Province, China.

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