MLHU redeclares Legionnaires’ outbreak in London, Ont., source identified

A fourth death has been connected to an outbreak of Legionnaires Disease in London.

After 25 additional cases of Legionnaires’ Disease were reported in London, Ont. the Middlesex-London Health Unit (MLHU) is redeclaring an outbreak, and the likely source has been confirmed.

“The decision to reopen the outbreak reflects a rise in cases after several weeks without new cases, suggesting that the Legionella bacteria has re-emerged in the environment despite earlier remediation efforts,” read a statement from the health unit.

During extensive case investigations, environmental sampling and collaboration with building operators, the health unit said multiple cooling towers at nine separate locations in London tested positive for live Legionella bacteria.

“Results from further testing at Sofina Foods Inc. were found to match the subtype linked to the outbreak,” said the health unit.

Despite routine cleaning and disinfection, the health unit added that trace bacteria can sometimes persist in cooling towers and regrow under hot, humid conditions.

Legionella bacteria occurs naturally in both soil and water, including environments such as hot tubs, cooling towers, hot water tanks, large plumbing systems and decorative pools or fountains.

According to the MLHU, Legionnaires’ disease is spread when people breathe in small water droplets containing the bacteria, like the vapour released from cooling towers.

The disease is not transmitted through eating or drinking, and food products from Sofina Foods Inc. remain safe to consume.

To date, the outbreak in 2025 has been linked to serious pneumonia in at least 94 London residents, resulting in 86 hospitalizations and four deaths.

When the outbreak was first declared over on Aug. 6, there had been 70 cases and three deaths.