Hamilton legionellosis outbreak over, public health officials say

This 2009 colorized 8000X electron micrograph image provided by the Centers for Disease Control and Prevention shows a large grouping of Gram-negative Legionella pneumophila bacteria. THE CANADIAN PRESS/AP-Janice Haney Carr

HAMILTON — Public health officials in Hamilton say a local outbreak of legionellosis, also known as legionnaires’ disease, is over.

Hamilton Public Health says that over roughly three weeks in May, 22 people in the east Hamilton and Stoney Creek areas were hospitalized after a lab confirmed their infections.

The agency says it declared the outbreak over after no additional cases were reported between May 26 and Saturday.

Legionnaires’ disease is spread by inhaling droplets containing the bacteria, with symptoms such as a high fever, chills, shortness of breath and a cough.

Officials say they investigated cooling towers and other sources that could be releasing droplets into the air outside but have not confirmed the source of the outbreak.

Public health authorities say that despite extensive investigation, the source of outbreaks is not always identified.

Hamilton’s associate medical officer of health, Dr. Brendan Lew, says residents and water system operators must make sure their equipment is properly used and maintained.

This report by The Canadian Press was first published June 29, 2026.

The Canadian Press