Etiological analysis on a bacillary dysentery outbreak caused by Shigella sonnei in Beijing

  Objective  To investigate the etiologic and epidemiologic characteristics of an outbreak of bacillary dysentery caused by Shigella sonnei in a boarding school in Beijing, China.

  Methods  Stool samples of the cases and cookers, water samples and environment smear samples were collected from 5^th to 20^th September, 2019 for pathogen isolation and identification. Drug susceptibility test, pulsed-field gel electrophoresis (PFGE), whole genome sequencing (WGS), multi-locus sequence type (MLST), drug resistance related gene and virulence gene detection were performed, and the phylogenetic tree was constructed by whole genome single nucleotide polymorphism (wgSNP).

  Results  In this outbreak, 16 Shigella sonnei strains and 1 enterotoxigenic Escherichia coli (ETEC) strain were isolated. The antibiotic susceptibility testing revealed that 16 S. sonnei isolates were resistant to ampicillin, tetracycline, trimethoprim and sulphame-thoxazole, cephazoline, cefotaxime, gentamicin, nalidixic acid, azithromycin, doxycycline. Further tests confirmed these isolates to be extended-spectrum beta-lactamase (ESBLs) producing strains. MLST unfolded that all isolated S. sonnei strains in this outbreak belonged to ST152, a common epidemic sequence type in China. An insertion sequence was found in a S. sonnei strain and the ETEC strain, but not in other S. sonnei strains.

  Conclusion  It was confirmed that the pathogen of this outbreak was S. sonnei. In addition to PFGE, WGS is necessary for epidemiological investigation.