Public Health declares end of Legionellosis outbreak

HAMILTON, ON – Hamilton Public Health (HPH) has declared the local outbreak of Legionellosis in East Hamilton/Stoney Creek over.

Between May 4 and May 26, 2026, 22 laboratory-confirmed cases of legionellosis associated with this outbreak were reported to HPH. All 22 lab-confirmed cases resulted in hospitalization. Cases ranged in age from their late 30s to their early 90s.

Given that no additional cases have been reported to HPH between May 26 and June 27, 2026, the outbreak has been declared over. HPH carried out a comprehensive investigation that included the assessment of nearby cooling towers and other potential sources that can release fine water droplets into the air outdoors. Although no confirmed source was identified, the time since cases have been reported suggests the risk of exposure has decreased.

In investigations of legionellosis outbreaks, a specific source of exposure is not always identified, despite extensive investigation and testing of potential sources and a thorough review of where exposure may have occurred. While a specific source may not be identified, follow-up has been done with operators of cooling towers and other potential sources that can release fine water droplets into the air to remind them to ensure that systems are in proper working order and maintained appropriately. 

“While this outbreak has been declared over, vigilance remains essential,” said Dr. Brendan Lew, Associate Medical Officer of Health. “Prevention is our most effective tool when it comes to reducing the risk of Legionellosis exposure. As temperatures rise and cooling towers are brought back into seasonal operation, residents and facility operators of water systems should ensure their equipment is properly maintained and operated. Regular inspection, cleaning and maintenance help prevent the growth of Legionella bacteria and play an important role in protecting the health and safety of our community.”

HPH will continue to monitor for and investigate reported cases of Legionellosis, and engage with operators, and municipal and provincial partners to reduce the risk in Hamilton. 

Quick Facts:

• The bacterium that causes Legionellosis is commonly found in the environment. The disease is not spread person to person, but rather occurs through inhalation of droplets containing the bacterium.
• Legionellosis symptoms include high fever, chills, shortness of breath and a cough. Medical examination and testing are needed to determine whether someone has pneumonia caused by the bacteria.
• Legionellosis occurs more often in individuals aged 50 and over, individuals with weakened immune systems such as organ transplant patients and individuals with lung conditions, cancer or diabetes, as well as smokers.
• Residents are reminded to regularly clean and maintain household water systems such as humidifiers and hot tubs.
• The City of Hamilton’s Cooling Tower Registry requires owners to register existing cooling towers, helping HPH staff promptly identify these systems and carry out assessments as appropriate.

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