Objective To analyze the etiological characteristics of a cholera epidemic in Tongzhou district of Beijing in 2022 and make a comparison with previous cholera epidemics in Tongzhou.
Methods The specific genes of Vibrio cholerae O1/O139 were detected by real-time PCR. At the same time, the strains were isolated, cultured and identified by conventional method. Eleven virulence genes of V. cholerae were detected by common PCR, and 12 kinds of drug sensitivity tests were carried out by minimal inhibitory concentration method. NotⅠ restriction enzymes were used for pulsed field gel electrophoresis (PFGE) analysis and cluster analysis. Genetic analysis on strains was performed by whole genome sequencing.
Results A total of 5 strains of non-virulence V. cholerae O1 serotype Ogawa were detected in this epidemic. All the strains carried ompU, toxR, tcpI, tcpAEL, hlyAEL, hlyACL and rtxC genes, but carried no ctxAB gene. The drug resistance of the 5 strains was consistent. All the strains were resistant to meropenem, cefotaxime, ceftazidime, streptomycin, ampicillin, and ampicillin/sulbactam. PFGE divided the strains into 6 types (Ⅰ– Ⅵ), and the strains causing this epidemic belonged to type Ⅱ. The comparison with the two strains of virulence V. cholerae O1 serotype Ogawa detected in previous local epidemic in 2011 indicated the similar PFGE pattern, the drug resistance was same, the virulence gene carriage was different, but both carried tcpAEL gene. Genetic analysis showed that the strains in this epidemic belonged to new and emerging clonal group which was different from the strain causing the 7th pandemic.
Conclusion The predominant V. cholerae O1 strain in Tongzhou belonged to serotype Ogawa without toxin producing. PFGE patterns varied. The strains detected in this epidemic belonged to a newly emerged clone group. In cholera prevention and control in the future, attention should be paid to these strains and targeted strategies should be developed.
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