See Region of Waterloo Public Health's Legionella Fact Sheet for a printable version of the information presented on this web page.

What is Legionellosis?

Legionella is a bacterium that lives in water and is found in both natural and artificial environments. Of the many species of Legionella, Legionella pneumophilia is the species that is commonly associated with Legionellosis, a serious disease in humans. Legionellosis is an acute infection of the lungs and has two forms: Legionnaires' disease, which is a severe type of pneumonia, and Pontiac Fever, which is a milder illness caused by the same bacteria.1

What are the symptoms?

Legionnaires' disease is a severe form of pneumonia. Symptoms of Legionnaires' disease include fever, cough, headache, weakness, muscle aches and pains, and chills. Symptoms usually develop two to fourteen days after being exposed to the bacteria. 2,1

Pontiac fever is a mild, self-limiting illness that typically resolves in one to three days without the need for medical care.1

Who is at risk?

The risk of becoming ill from Legionella is quite low for healthy people. Generally, men are more likely than women to develop the disease. Groups that are at an increased risk if exposed to Legionella bacteria include: 

  • People over 50 years of age, especially men 
  • Smokers 
  • People with diabetes 
  • People with chronic obstructive pulmonary disease or kidney disease 
  • People with weakened immune systems (e.g., due to cancer or an organ transplant)

How do I know if I have Legionellosis?

If you have any symptoms you should seek medical attention immediately. Laboratory tests are available to determine if you have the disease.

How is Legionellosis treated?

Legionnaires' disease is usually successfully treated with antibiotics, however, people with any of the risk factors listed above may have a longer recovery period.

How is it spread?

  • Legionella is not spread from person to person 
  • People acquire the illness by breathing in water droplets or mist contaminated with Legionella
  • Legionella bacteria are naturally found in many environments, especially in warm water sources where biofilms can develop1 
  • Cases and outbreaks of Legionellosis tend to occur in the late summer and fall1 
  • Some common sources of Legionella include 1,3
    • Natural: lakes and rivers 
    • Home: hot tubs, whirlpools, hot water tanks, air conditioners, humidifiers, shower heads, faucets, respiratory therapy equipment, decorative fountains; damp potting soil or compost 
    • Commercial/Public: cooling towers, heating, ventilation, and air conditioning systems, public hot tubs or whirlpools

What factors favour the growth of Legionella?3

  • Warm temperatures - Legionella can survive and multiply in water at temperatures of 25-45┬░C (68┬░F-113┬░F) for several hours3 
  • Humidity 
  • Stagnant water 
  • Biofilms (a thin, slimy film of bacteria that can build on the surface of stagnant water)

What can I do in my home to protect myself from Legionellosis?

In your home, follow manufacturers' directions for the regular cleaning and disinfection of all water devices that may produce aerosolized water (mist) such as hot tubs, whirlpools, humidifiers, air conditioners, shower heads, respiratory equipment, and decorative fountains.

When possible, avoid water temperatures between 25┬░C and 45┬░C (68┬░F-113┬░F) to prevent Legionella colonization/ multiplication. It is not always practical to avoid lukewarm water temperatures. Therefore, it is important that you keep water devices clean.

For information on hot tubs and Legionella, check the Hot Tubs and Legionella Fact Sheet.

Note: Tap water should not exceed 49┬░C in order to avoid burning/scalding.

Information for Commercial/Public Access to Water Systems

If you are involved in the maintenance, operation, or ownership of cooling towers or hot water systems, access the following resources for additional information to prevent the growth and spread of Legionella bacteria.

Legionellosis Guidelines: Best Practices for Control of Legionella (Cooling Technology Institute) 

ASHRAE Guideline 12-2000: Minimizing the Risk of Legionellosis Associated with Building Water Systems 

Ontario Building Code Act, Ontario Regulation 23/04 - this regulation ( notes that the maximum temperature of water "supplied by fittings to fixtures in a residential occupancy shall not exceed 49┬░C."4

Public Spa, Ontario Regulation 428/05 - this regulation notes that for water treatment, "there is a residual of free available chlorine or total bromine of at least five but not more than 10 milligrams per litre."5


  1. Ministry of Health and Long-Term Care. (2013). Ontario Public Health Standards: Infectious Diseases Protocol, 2013. Appendix A: Disease-Specific Chapters: Legionellosis. Toronto, ON: Queens Printer for Ontario.
  2. Public Health Agency of Canada. (2014). Legionella.
  3. Building Code Act, 1992. Ontario Regulation 23/04, Building Code.
  4. Health Protection and Promotion Act. Ontario Regulation 428/05, Public Spas.