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Middlesex-London Health Unit

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Cooling Towers and Legionellosis

Cooling towers and systems have been implicated as causes of Legionella infections (legionellosis) in residential, occupational and other public settings.  Research has shown that a thorough Legionella control program can greatly reduce the risk of cooling equipment causing a Legionella infection.1

What is Legionella?

Legionellae are bacteria that are commonly present in natural and man-made environments.2 The organism is occasionally found in other sources, such as mud from streams and potting soils.2 Equipment such as cooling towers, hot water tanks, shower heads, large plumbing systems, whirlpool spas, hot tubs, and air conditioning systems of larger buildings have all been found to be periodic sources of exposure to Legionella.

What is legionellosis?

Legionellosis is an acute bacterial disease that can lead to two types of illnesses called “Legionnaires’ Disease” and “Pontiac Fever.”3

Humans may get legionellosis if droplets of water containing Legionella are breathed in. Persons over 50, smokers and persons whose immune system is compromised are most at risk.3

To learn more, read the Middlesex London Health Unit’s Legionnaires’ Disease web page. Visit the Government of Canada’s Legionella web page to find additional information about legionellosis, how is spreads, symptoms, risk factors, and how to reduce your risk.

How common are legionellosis outbreaks?

Historically in Middlesex-London, Legionnaires’ disease cases have been sporadic (single cases not occurring as part of an outbreak).

According to Agence de la santé et des services sociaux de la Capitale-Nationale, Communique de presse, September 19, 2012 an outbreak of Legionnaires’ disease in Québec resulted in the deaths of 13 persons and 180 confirmed cases of persons becoming ill.4 A cooling tower was at fault being genetically linked to the ill persons.4

Additional Information

For more information or questions about cooling towers and systems, or the Cooling Tower Registration Project, please continue to browse this website, or

Date of creation: April 11, 2013
Last modified on: January 3, 2018


1Cooling Technology Institute. (2008, July). Legionellosis: Guideline: Best practices for control of Legionella. Houston, TX: Cooling Technology Institute.
2American 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.
3Heyman, D.L. (Ed.). (2014). Control of communicable diseases manual (20th ed.). Washington, DC: American Public Health Association Press.
4Agence de la santé et des services sociaux de la Capitale-Nationale. (2012, September 19). Communiqué de presse: Le Directeur de santé publique identifie une concordance entre la bactérie qui a affecté des personnes et celle contenue dans dans un échantillion prélevé dans une tour de refroidissement. Retrieved from