Shiga Toxin 1–ProducingShigella sonneiInfections, California, United States, 2014–2015

Abstract

Shiga toxins (Stx) are primarily associated with Shiga toxin–producing Escherichia coli and Shigella dysenteriae serotype 1. Stx production by other shigellae is uncommon, but in 2014, Stx1-producing S. sonnei infections were detected in California. Surveillance was enhanced to test S. sonnei isolates for the presence and expression of stx genes, perform DNA subtyping, describe clinical and epidemiologic characteristics of case-patients, and investigate for sources of infection. During June 2014–April 2015, we identified 56 cases of Stx1-producing S. sonnei, in 2 clusters. All isolates encoded stx1 and produced active Stx1. Multiple pulsed-field gel electrophoresis patterns were identified. Bloody diarrhea was reported by 71% of case-patients; none had hemolytic uremic syndrome. Some initial cases were epidemiologically linked to travel to Mexico, but subsequent infections were transmitted domestically. Continued surveillance of Stx1-producing S. sonnei in California is necessary to characterize its features and plan for reduction of its spread in the United States.

Recent Outbreaks of Shigellosis in California Caused by Two Distinct Populations of Shigella sonnei with either Increased Virulence or Fluoroquinolone Resistance

“…SDi and SJo isolates constituted the same outbreak population, which was incongruent with two separate clusters identified by PFGE (15). Many recent publications have highlighted superior discriminatory power and predictive value of whole-genome sequencing (WGS) over PFGE for genotyping of bacterial strains (34).…”

“…Shiga toxin production by SDi/SJo isolates harboring stx1 genes was confirmed in Vero cell neutralization assay. The data were presented in an earlier publication by Lamba et al (15). None of the historical isolates or recent isolates related to the San Francisco outbreak had stx genes.…”

“…Isolates from the SDi/SJo S. sonnei population, which caused outbreak of severe diarrheal disease (15), carried stx1 genes carried on a novel lambdoid bacteriophage in all of the isolates. The strains of E. coli O104:H4 serotype appeared to be the most likely source of the STX bacteriophage in SDi/SJo S. sonnei isolates based on overall similarity of their whole-phage sequences.…”

“…The first outbreak with distinct clusters in the San Diego and San Joaquin (SDi/SJo) areas was caused by STX-producing isolates (15). Another CA S. sonnei outbreak occurred within the same time frame as the two clusters described above, but it was caused by an STX-negative S. sonnei strain and was confined primarily to the San Francisco (SFr) Bay area (16).…”

An Update on Aptamer-Based Multiplex System Approaches for the Detection of Common Foodborne Pathogens

“…Furthermore, other Shigella sp. like S. sonnei is currently causing foodborne disease with shiga toxin production (Lamba et al 2016). Our group developed a more simplified S. sonnei sandwich detection system.…”