Reports of Legionella related illnesses increase in the summer. In the last three years, surveillance data indicates annual increases of reported Legionella related illnesses in both Toronto and Ontario overall. The majority of cases occur between August and October, corresponding to periods of warmer weather.

In response, the Ontario Chief Medical Officer of Health, Dr. Arlene King called on all Ontario Health Units to provide guidance information for the prevention of Legionella in cooling towers and other water systems within their communities. For more information on Legionella and Legionellosis, please see this fact sheet.