A Canadian tofu Salmonella outbreak is the first of its kind, according to the CDC‘s Morbidity and Mortality Weekly Report for August 11, 2023. Salmonella Typhimurium was the serovar that made people sick. About 38 people in 10 public health districts in Ontario, Canada were sickened.
Officials concluded that lapses in sanitation and recommended heat processing likely resulted in the contamination. Tofu has not been linked to nnontyphoidal Salmonella outbreaks before. This outbreak should serve as a warning to consumers, processors, and retailers that Salmonella can be transmitted through ready to eat soy products.
From May to mid-August 2021, Public Health Ontario investigated a cluster of 38 patients with Salmonella Typhimurium infections. Five of the patients were hospitalized.
The outbreak was linked to consumption of ready-to-eat seasoned tofu from one manufacturer that was distributed to multiple Ontario restaurants. Testing found that isolates from the seasoned tofu were within one or fewer allele differences to the outbreak strain according to whole genome sequencing.
Evidence from investigations conducted by the Canadian Food Inspection Agency and local public health authorities revealed that unsanitary conditions could have led to cross-contamination of the tofu. Then, insufficient heating of the tofu at the production level failed to eliminate the pathogen. Tofu was identified as a novel outbreak-associated food vehicle for this outbreak.
Illness onset dates were from May 16 to July 31, 2021, suggesting an ongoing common source. Thirty patients were interviewed and said they were on a vegetarian or vegan diet. Among the 25 patients who provided a response for “consumption of tofu” on a survey, 19, or 76%, reported that they had consumed or probably consumed tofu, which was a much higher proportion than the general population.
Among the 19 patients who said they consumed tofu, 16 said they purchased seasoned tofu either at one of 11 restaurant franchise locations or one of three non franchise restaurant locations in Ontario before they got sick. Investigators looked at restaurants where consumers ate, and found a common tofu manufacturer. Salmonella Typhimurium was isolated from three open specimens of seasoned tofu from one of the restaurant franchise locations. That pathogen was closely related by whole genome sequencing to patient isolates.
In addition to the inadequate heat treatment for the tofu at the manufacturer’s facility, investigators found poor sanitation of the processing equipment, the absence of a food safety plan, and no food sampling program. A heat treatment step after seasoning was applied to the tofu was instituted at the manufacturing facility.
Novel outbreak-associated food vehicles can emerge because a pathogen can evolve, or through a change in dietary habits and trends. The implication of this outbreak is of public health importance because of the global increase in the consumption of plant-based proteins and the long term ramifications of a Salmonella infection.
Osasah V, Whitfield Y, Adams J, Danish A, Mather R, Aloosh M. An Outbreak of Salmonella Typhimurium Infections Linked to Ready-To-Eat Tofu in Multiple Health Districts — Ontario, Canada, May–July 2021. MMWR Morb Mortal Wkly Rep 2023;72:855–858. DOI: http://dx.doi.org/10.15585/mmwr.mm7232a1.
