Listeria monocytogenes, the bacteria that cause listeriosis, are hardy pathogens that can survive refrigeration and freezing. Major outbreaks of listeriosis have been linked to cantaloupe, soft cheeses, ice cream, chocolate milk and cold cuts, among other food and drinks.Elizabeth White/The Canadian Press
Federal public-health officials were aware of two genetically related cases of listeriosis last September, but were unable to trace their source to an Ontario factory making plant-based milks until more people fell ill with the potentially fatal bacterial infection last month.
The Public Health Agency of Canada shed more light Thursday on the investigation into the listeriosis outbreak, which has killed two people and sickened at least 10 others who drank refrigerated alternative milks that have since been pulled off store shelves across the country.
PHAC announced the deaths on Wednesday night, and the Ontario Ministry of Health confirmed Thursday morning that the deceased were from its province.
Eight other Ontarians, one Nova Scotian and one Quebecker are known to have fallen ill in connection with an outbreak that the Canadian Food Inspection Agency (CFIA) traced to alternative milks from Silk, a unit of the French food maker Danone, and Great Value, a brand sold at Wal-Mart. Most were over the age of 60 and female.
The CFIA had announced a recall of 18 different types of refrigerated plant-based milks from the two brands – including almond, cashew, oat and coconut milk – on July 8.
Jennifer Vincent, a spokesperson for Danone Canada, said Thursday that the CFIA made the company aware of the listeria contamination over the weekend of July 5. That prompted Danone to issue a voluntary recall to all the stores that sold Silk and Great Value plant-based milks made on one production line at the third-party factory where the outbreak is believed to have originated.
Ms. Vincent confirmed that the factory is in Ontario but declined to name it.
Listeria monocytogenes, the bacteria that cause listeriosis, are hardy pathogens that can survive refrigeration and freezing. Major outbreaks of listeriosis have been linked to cantaloupe, soft cheeses, ice cream, chocolate milk and cold cuts, among other food and drinks. A 2008 outbreak that began at a Maple Leaf Foods plant in Toronto killed 22 people, the deadliest such outbreak in Canadian history.
Tracing listeria outbreaks can be challenging, said Vanessa Allen, a medical microbiologist and infectious disease doctor at Sinai Health and University Health Network in Toronto.
Most people who ingest the bacteria don’t get sick. Others develop mild gastroenteritis. Typically, it is only when newborn, elderly or immunocompromised patients develop invasive listeriosis – a potentially fatal infection of the bloodstream or neurological system – that cases come to the attention of public-health officials.
PHAC estimates there are about 134 cases of invasive listeriosis in Canada every year.
“It’s a very stealthy organism,” Dr. Allen said. The incubation period for invasive cases can be as long as 70 days, she added, which can make it difficult for patients to pinpoint the food or drink that made them sick.
That could help explain why, according to PHAC, two patients linked to the outbreak became sick as far back as last August, nearly a year before the recall.
Anna Maddison, a spokesperson for PHAC, said by e-mail Thursday that the agency was made aware of those cases last September. PHAC concluded through whole genome sequencing of the culprit bacteria that the cases were genetically related to each other.
However, “no common food exposures were identified at the time, nor were any identified when a third case was reported in January 2024,” Ms. Maddison said.
“When additional cases were reported in a single province in Canada in June 2024, a provincial investigation identified the source of the illnesses to be plant-based refrigerated beverages, which were recalled on July 8, 2024.”
Investigators re-contacted the patients who fell ill earlier and determined they, too, drank the “implicated beverages,” Ms. Maddison added.
The beverages named in the recall notice had best before dates as late as Oct. 4, 2024. People who drank the potentially contaminated milks need not worry unless they start to feel sick with a fever or flu-like symptoms, Dr. Allen said. In that case, she said, they should seek medical attention, particularly if they are senior citizens, immunocompromised or pregnant.
Invasive listeriosis is fatal in 10 to 40 per cent of cases, Dr. Allen said, but it can be treated in hospital with IV antibiotics. The infection raises the risk of miscarriage or stillbirth in pregnant women.