The local outbreak of Legionnaires’ Disease has been declared over.
Between July 8 and August 6, 2025, a total of 70 confirmed legionella cases met the criteria for inclusion in the outbreak. Nearly all (91% or 64) have been hospitalized, and three people have died. Currently, one case remains in hospital.
Given the substantial period of time that has passed since any new cases developed symptoms, the outbreak is considered over. At this time, a point source of the legionella bacteria has not been identified. Despite collecting 126 environmental samples from 26 cooling tower sites, all close to the geographic centre of the cases, no samples have yet detected legionella bacteria that is a match for that identified in the cases.
The search for a source will continue, with environmental sampling continuing for the remaining of the summer and fall.
What does this mean for the community?
Prevention is key. As temperatures rise and cooling towers are brought back into operation each year, property owners and operators of water-cooling systems are reminded of the importance of regular maintenance in line with applicable regulations. Proper system upkeep helps eliminate potential sources of Legionella bacteria and plays a vital role in protecting community health.
At this time we will no longer be updating the webpage for Confirmed Legionnaires’ Disease Cases in the Middlesex-London Region. However, the page will remain available for reference.
Frequently Asked Questions
How can the outbreak be over if the source has not been found?
The outbreak is being declared over now because no new cases have developed symptoms since July 9, 2025. This indicates that although a source has not yet been identified, the risk of exposure has decreased.
Will the source be found?
Similar to last year, the source of the Legionella bacteria has not been identified at this time. This can happen for a few reasons: the bacteria are hard to find, people may have been exposed to more than one source, or cleaning may have happened before testing.
To learn more about Legionnaire’s Disease and ways to prevent Legionella at home and in our community, visit: www.healthunit.com/legionnaires-disease.