Middlesex-London Health Unit Redeclares Legionnaires’ Disease Outbreak Following 25 New Cases; Likely Source Identified
Posted by Middlesex-London Health Unit on August 26, 2025
The Middlesex-London Health Unit (MLHU) is redeclaring the outbreak of Legionnaires’ Disease in London, following confirmation of 25 additional cases. 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. 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.
Legionella bacteria occur naturally in soil and water, especially warm water. They can contaminate and grow in environments such as hot tubs, cooling towers, hot water tanks, large plumbing systems, parts of air-conditioning systems in large buildings, and decorative pools or fountains.
During extensive case investigations, environmental sampling, and collaboration with building operators, 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. Despite routine cleaning and disinfection, trace bacteria can sometimes persist in cooling towers and regrow under hot, humid conditions. Earlier testing at the facility in 2024 and early 2025 did not produce a match. 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.
“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,” says Dr. Joanne Kearon, Associate Medical Officer of Health for the Middlesex-London Health Unit. “Fortunately, a likely source has now been identified.”
The MLHU is working diligently to ensure comprehensive remediation, with the goal of preventing additional cases. The operator has been fully cooperative throughout the outbreak, following required protocols, and taking every necessary step to complete thorough remediation.
The Health Unit will also continue to provide education and guidance to cooling tower operators across London and Middlesex County ahead of each Legionella season.
Legionnaires’ disease is spread when people breathe in small droplets of water containing the bacteria, such as those released from cooling towers. It is not transmitted through eating or drinking, and food products from Sofina Foods Inc. remain safe to consume.
The Health Unit will resume posting updated case counts for the Legionnaires’ Disease outbreak on the
website. Updates will be provided weekly on Tuesday afternoons.
Read more about Legionella and Cooling Towers, here:
www.healthunit.com/health-hazards#legionella.
https://www.healthunit.com/news/middlesex-london-health-unit-redeclares-legionnaires-disease
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Confirmed Legionnaires’ Disease Cases in the Middlesex-London Region
The Middlesex-London Health Unit is providing an update to the community following the redeclaration of the
Legionnaires’ Disease outbreak. A source for the outbreak has now been identified and remediation is underway.
Please note: Data will be updated each week on Tuesday afternoons.
Outbreak-Associated Case Details
Data extracted: August 26, 2025 (8:30am)
https://www.healthunit.com/confirmed-legionnaires-disease-cases
