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.

The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) defines a cooling tower as:

an evaporative heat transfer device in which atmospheric air cools warm water, with direct contact between the water and the air, by evaporating part of the water. Air movement through such a tower is typically achieved by fans, although some large cooling towers rely on natural draft circulation of air.

Adapted from American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE). (2000). ASHRAE guideline 12-2000: Minimizing the risk of Legionellosis associated with building water systems. Atlanta, GA: American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc.

  • Follow the equipment manufacturer maintenance instructions specific to the operation of atmospheric cooling towers, hot water systems and hydro-massage tubs.
  • Use precaution and ensure safeguards are in place and when shutting down equipment.
  • Ensure proper cleaning of the apparatus prior to re-start.
  • Be aware of and respond to adverse situations including:
    • changes in the functioning of the equipment.
    • external influences such as nearby construction causing increased dust entering
      into the cooling towers.

Toronto Public Health Strongly Urges Compliance with Industry Best Practices/Standards.