A deadly Listeria outbreak that contaminated plant-based milk in 2024 was traced back to a Pickering, Ont., plant thanks to a coconut beverage “past its expiry date” found in someone’s fridge, according to a recent investigation. In 2024, a recall was issued for several plant-based milk products under the Silk and Great Value brands amid concerns of listeria contamination. The outbreak was ultimately traced back to a production line at Joriki, the third-party facility in Pickering that packaged soy, almond and coconut beverages under the Great Value and Silk brands. The outbreak led to 20 reported illnesses. Fifteen people were hospitalized and three others died from the outbreak. The Pickering production line immediately shut down after the recall and never reopened its doors. Public Health Ontario published a research paper in June investigating the incident, as plant-based milks historically weren’t on their radar for listeria risk in the same way soft cheeses or deli meats have been. “This wasn’t one that was on our typical suspect food list, but we have seen (listeria) in pasteurized products before,” Dr. Christine Navarro, a public health physician at Public Health Ontario, said in an interview with CTV News. The outbreak bacteria was first detected in an open, leftover container of a coconut beverage found in a patient’s fridge, according to the peer-reviewed study. PHO says the beverage was “past its expiry date.” Navarro said that an investigator spotted the product in the fridge, learned that the patient consumed it recently and ultimately decided to bring it back to a lab for testing. “They talked about it with our Public Health Ontario laboratory colleagues and they suggested, ‘Yep, take a sample, bring it in,’” Navarro said. Samples can also be collected from a manufacturing facility or from grocery stores. While the samples that were initially collected at retail stores tested negative for Listeria, the investigation noted there were environmental swabs taken throughout the Pickering plant and that two of the swabs tested positive for listeria and were a genetic match to the outbreak strain. Those swabs, the report states, were found at a case packer area drain and a processing line drain cover in the post-pasteurization areas of the facility. The post-pasteurization process is typically effective at reducing Listeria contamination, Navarro noted. “When it’s found in the post-pasteurization area, that suggests that perhaps there’s some cross-contamination from other parts of the facility,” she said. “We know that Listeria can be very pervasive, it can be very stubborn.” Food-borne bacteria can hide in biofilms, Navarro explains. A biofilm is a community of microorganisms that attach to the surface and protect themselves in a self-made, glue-like matrix made up of sugars, proteins and other molecules that can make them challenging to fully remove. “Even if you do some routine cleaning, you may not be able to really reach every single nook and cranny where Listeria is hiding,” Navarro said. While investigators could not pinpoint exactly how the bacteria entered the products, every contaminated sample traced back to the same production line at the Pickering facility. Because of how ubiquitous Listeria can be, Navarro stressed it is important for manufacturers to adhere to Health Canada’s policies to protect Canadians with ready-to-eat foods. “It is difficult to really locate where the contamination occurred because it can be so ubiquitous and so stubborn once it is hiding in a biofilm in a drain or in a manufacturing line, it may be difficult to consistently detect,” Navarro said. “It may be only shedding from the biofilm intermittently, which we think is possibly what happened here.” The key takeaways The outbreak strain first popped up in August of 2023, but the investigation noted there were few cases and no leading hypothesis. Nearly a year later, the report says the strain-remerged due to routine leftover food sample collection. In this instance, the investigation determined that leftover food sample collection and testing were instrumental in identifying the outbreak source in a timely manner. The CFIA was able to issue a food recall within two weeks of the initial match. Navarro also urges public health investigators to stay vigilant about novel food sources. Though plant-based milk wasn’t among their common list of culprits before, Navarro noted that there had been an outbreak in pasteurized products in the past, pointing to a listeria outbreak in chocolate milk a decade ago. “Because of the collaboration of the investigator and the laboratory, we were able to find this item and initiate a recall,” Navarro said of how the plant-based beverage recall was triggered. It is also imperative for those who are immunocompromised to stay vigilant with the products that they consume, particularly if the food items are at high risk of being contaminated with listeria. “Things like ready-to-eat meats, like cold cuts, soft cheeses, unpasteurized dairy products, those are things that people should be aware of,” Navarro said. With files from The Canadian Press
