The local outbreak of Legionnaires’ Disease, declared by the Middlesex-London Health Unit in July, has slowed but is ongoing. Its source continues to elude investigators.

Between May 1 and September 26, 2024, a total of 30 confirmed legionella cases met the criteria for inclusion in the outbreak. The individuals infected by the legionella bacteria ranged in age from 37 to 76 and more than half (19) were males. All 30 have been hospitalized at some point, nine were admitted to the Intensive Care Unit, and two cases have died. Four cases remain in hospital.

Despite collecting environmental samples from 17 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.

“It is common in an investigation such as this one that the source of the legionella bacteria that has caused the outbreak cannot be found. We conducted our search based on the location of the cases, wind and weather patterns and the types of cooling towers in the region. Unfortunately, while some legionella was identified, none of it linked back to the cases,” explains Dr. Joanne Kearon, Acting Medical Officer of Health for the Middlesex-London Health Unit.

“It’s frustrating. We all like situations like this to come to a satisfying conclusion. Instead, what we can emphasize is the importance of prevention. We ask that all businesses and property managers with cooling towers or other susceptible pieces of equipment ensure they are properly maintained throughout the year,” adds Kearon.

Though the source may not be found, transmission is slowing and the outbreak may soon be declared over.

Media Contact:
Megan Cornwell, Corporate Communications Manager
media@mlhu.on.ca

Spokesperson:
Dr. Joanne Kearon, Acting Medical Officer of Health