An Outbreak of Salmonella Typhimurium Infections Linked to Ready-To-Eat Tofu in Multiple Health Districts-Ontario, Canada, May-July 2021

From May to mid-August 2021, the Ontario, Canada provincial public health agency, Public Health Ontario, in collaboration with local public health authorities and federal food safety partners, investigated a spatiotemporal cluster of 38 patients with Salmonella Typhimurium infections across multiple public health districts in Ontario. Five (13%) patients were hospitalized; no deaths were reported. The outbreak was linked to consumption of ready-to-eat seasoned tofu from one manufacturer that was distributed to multiple Ontario restaurants. Isolates from the seasoned tofu were within one or fewer allele differences to the outbreak strain by whole genome sequencing. Evidence from food safety investigations conducted by local public health authorities and the Canadian Food Inspection Agency (CFIA) revealed that unsanitary con-ditions could have led to cross-contamination of the tofu, and insufficient heating of the tofu at the production level likely resulted in failure to eliminate the pathogen. The CFIA issued a food recall for the tofu at hotel, restaurant, and institution levels. Tofu was identified as a novel outbreak-associated food vehicle for S. Typhimurium in this outbreak. Interventions that target the production level and all parts of the supply chain and include additional safeguarding steps that minimize microbial growth are important.an outbreak investigation. Cases continued to be reported across Ontario through mid-August; among 10 public health districts, incidence ranged from <= 0.2 to 2.9 cases per 100,000 persons. Although S. Typhimurium is one of the most com-mon serovars in Ontario, the outbreak strain was not related to any existing clusters or isolates in PulseNet Canada, a national surveillance system that collects information on foodborne-related illnesses caused by specific pathogens. This activity did not require ethics approval because the operations were within the purview of PHO's legislated mandate.* PHO defined a confirmed case as an infection with S. Typhimurium in a resident of or a visitor to Ontario occur-ring after April 30, 2021, with a genomic sequence pattern consistent with (<= 10 wgMLST allele differences) the outbreak strain. Thirty-eight cases were reported across 10 of 34 public

Automated summary

From May to mid-August 2021, a Salmonella Typhimurium outbreak occurred in Ontario, Canada, linked to consumption of seasoned tofu from a specific manufacturer. Investigations revealed unsanitary conditions and insufficient heating during production as potential causes of cross-contamination and pathogen survival. Tofu was identified as a novel outbreak-associated food vehicle for S. Typhimurium.