Likely source of legionnaires’ disease found in London, Ont., as outbreak redeclared

Public health officials in London, Ont., have redeclared an outbreak of legionnaires’ disease after confirming 25 new cases and identifying the likely source of the bacteria.

The Middlesex-London Health Unit said Tuesday that testing at the Sofina Foods plant in the city’s east end found a match to the subtype of legionella bacteria linked to the outbreak.

Food products from Sofina Foods remain safe to eat, the health unit said, as legionnaires’ disease is spread when people breathe in small droplets of water containing the bacteria and it’s not transmitted through eating or drinking.

Legionella bacteria occur naturally in soil and water and can grow in places such as cooling towers, hot water tanks and air-conditioning systems in large buildings. The health unit has previously said that it found legionella bacteria in multiple cooling towers in London, but those samples did not match the cases in the outbreak.

So far this year, the outbreak has been linked to “serious pneumonia” in at least 94 people, resulting in four deaths and 86 hospitalizations.

The health unit previously declared an end to the outbreak on Aug. 6, after reporting that no new cases had developed symptoms since July 9.

“For several weeks, no additional illnesses were reported, and we were optimistic that remediation efforts had eliminated the bacteria. However, 25 more people have now become ill,” Dr. Joanne Kearon, associate medical officer of health, said in a news release Tuesday.

While earlier testing at the Sofina Foods plant in late 2024 and early 2025 did not produce a match, health officials say trace bacteria can persist in cooling towers and regrow in hot, humid conditions.

“In the last month, two rounds of testing were conducted; the first showed no match, while the second did, most likely because of bacterial regrowth between the tests,” the health unit said in the release.

Sofina Foods said the latest test results were “unexpected,” given the negative results from previous tests and the daily safety and sanitation measures it has in place.

“We are deeply concerned with this new information and we are continuing to investigate this fully,” Sharon Begley, chief safety officer of Sofina Foods, said in a statement Tuesday.

The company said it is conducting further deep cleaning and disinfecting recommended by the health unit and will keep its cooling tower off-line until cleaning is complete.

The health agency said the building operator has been “fully co-operative” throughout the outbreak by following required protocols.

This report by The Canadian Press was first published Aug. 26, 2025.