The Lengthy Process of Connecting Multiple Listeria Cases to Certain Plant-Based Milks

Only when a cluster of Listeria cases surfaced in Ontario did the federal health agency manage to trace the source of an outbreak now tied to three deaths and 20 infections.

Since the Canadian Food Inspection Agency declared a national recall of multiple Silk and Great Value plant-based milk products on July 8, questions have lingered about why it took nearly a year to remove affected items from store shelves.

Health experts suggest that various factors complicated efforts to pinpoint the origins of this particular outbreak, such as the uncommon occurrence of Listeria in plant-based beverages and the lengthy incubation period of listeriosis cases caused by Listeria bacteria.

“It’s akin to solving an epidemiological puzzle where all the pieces need to fit together before the bigger picture emerges,” explains Lori Burrows, a microbiologist at McMaster University in Hamilton.

According to the Public Health Agency of Canada, the connection between a Listeria case reported in August 2023 and a larger outbreak was only established after multiple infections arose in Ontario in June 2024.

The federal health agency states that it first became aware of two genetically linked listeriosis cases in September 2023 but found no common food exposure among them.

However, when nine cases were reported in Ontario many months later, a provincial investigation was initiated, cites agency spokesperson Anna Maddison.

“Investigators managed to contact the cases from 2023 again and establish that they had also consumed the implicated beverages prior to falling ill,” Maddison stated in an email on Wednesday.

By the latest update on Monday, Canada had recorded 20 cases, with infected individuals in Ontario, Quebec, Nova Scotia, and Alberta. In Ontario alone, three deaths have been linked to the outbreak, including two in Toronto, as per the city’s public health agency.

The origin of the illness has been pinpointed to a specific production line at a third-party beverage packaging facility in Pickering, Ont., utilized by plant-based milk producer Danone Canada.

The facility was closed on July 6, and production has ceased since then.

Danone’s head of communications mentions that the company is intensifying testing for all refrigerated products at its other facilities.

“Throughout the investigation, we are seeking assistance from independent experts in addition to collaborating with health authorities to uncover the cause of contamination,” Jennifer Vincent shared in an interview on Wednesday.

A timeline provided on the federal health agency’s website notes the first case reported in August 2023, followed by a second in September and a third in December. Subsequently, a surge of nine cases came in June, with eight more in July of this year.

Symptoms of a Listeria infection may take up to 70 days to manifest, making it challenging to swiftly identify these types of outbreaks, mentions Lawrence Goodridge, a professor and Canada research chair in foodborne pathogen dynamics at the University of Guelph.

“At that point, individuals may struggle to recall what they consumed and when,” Goodridge adds.

The recalled products include Silk almond milk, coconut milk, almond-coconut milk, oat milk, and almond-cashew milk, as well as Great Value almond milk with best before dates up to and including Oct. 4 and containing 7825 in the product code.

In contrast to deli meats or unpasteurized cheese, food items more commonly associated with Listeria, a plant-based product might not have been on anyone’s radar, suggests Burrows.

“To find it in a beverage is unusual, and to have it in a plant-based beverage is unique because individuals usually perceive them as healthy alternatives,” Burrows points out.

Goodridge concurs, stating, “To my knowledge, this is the first instance of almond milk being linked to Listeria or any foodborne outbreak for that matter.”

Vincent mentions that Silk’s refrigerated plant-based beverages are back on retail shelves after increased production at other facilities.

“Our investigation is still ongoing. We are deeply saddened by this occurrence and offer our apologies for the situation,” Vincent concludes.