Food poisoning from raw horse meat contaminated with Shiga toxin-producing <i>Escherichia coli</i> O157 linked to nationwide spread of closely related strains, Japan, 2023

Investigations of Shiga toxin-producing <i>Escherichia coli</i> (STEC) foodborne outbreaks incorporating whole-genome sequencing (WGS) have not been widely conducted to date. This study demonstrated that the combination of multilocus variable-number tandem-repeat analysis, WGS, and nationwide surveillance allowed for the detection of a dispersed STEC O157 outbreak linked to raw horse meat. Simultaneously, the investigation suggested persistent and low-diversity contamination at a single meat shop over a 1-year period. This study highlights (i) how combining genomic analysis with epidemiological investigation can identify geographically widespread STEC cases, (ii) the risk posed by inadequate hygiene management in facilities producing meat for raw consumption, and (iii) the potential for STEC strains to persist with minimal genomic mutations in food or processing environments. These insights support targeted control measures such as improved sanitation, the implementation of hazard analysis and critical control point principles, and ongoing genomic surveillance to prevent similar outbreaks.