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Legionnaires Disease and Pontiac Fever

Legionella pneumophila bacteria

Legionnaires' disease and Pontiac fever are both forms of a disease called legionellosis, an uncommon respiratory infection caused by Legionella pneumophila bacteria. Water systems and devices can spread Legionella to people, with one of the most common ways to get sick is by breathing in aerosolized water containing the bacteria. 

Information for Health Professionals

Legionella are bacteria that infect the lungs. When a person gets sick from this infection it is called legionellosis. The serious form of legionellosis is called legionnaires’ disease. A milder form of the infection is called Pontiac fever. 

From January 1, 2019-December 31, 2023, 85 cases have been reported to the BC Centre for Disease Control. 


The most significant cause of legionellosis is the bacterium Legionella pneumophila. The bacteria are naturally found in the environment, most often in water. People become infected when they breathe in spray or mist coming from contaminated water. Legionella grows best in standing water at 20-50°C. Legionella infections are not usually spread from person to person.

There have been individual cases and outbreaks linked to these water systems and devices:

  • Wet cooling towers (structures that use water and a fan to cool centralized air systems for buildings or industrial processes). 
  • Hot tubs, jacuzzis, or whirlpools.
  • Decorative fountains and water features.
  • Aerosol generating equipment (i.e., humidifiers or misters).
  • Devices that do not pose an infection risk: Home and car air-conditioning units do not use water to cool the air and therefore are not a risk for Legionella growth. This includes window units commonly found in some hotels.
People at most risk of infection and serious illness from a legionella infection are:
  • Those over the age of 50
  • Current or former smokers
  • Those who have a lung disease such as emphysema
  • Chronic conditions such as diabetes
  • Those whose immune system is compromised (e.g., cancer)

Legionnaires’ disease produces symptoms similar to pneumonia, including:

  • Loss of appetite 
  • Muscle pain 
  • Headache, followed by: 
  • High fever
  • Chills
  • Cough 
  • Abdominal pain, and 
  • Diarrhea

Symptoms start an average of 5 to 6 days (range 1 to 19 days) after exposure to the bacteria. 

Pontiac fever causes mild symptoms of:

  • Fever
  • Headache, and
  •  Muscle aches that go away without serious problems.

Symptoms start an average of 24 to 48 hours (range 5 to 66 hours) after exposure to the bacteria. Sometimes a person can be infected and have no symptoms.


If you think you have a legionella infection, see your family doctor immediately for testing, advice and treatment. Contact your local environmental health officer to discuss where the infection might have come from, especially if you suspect a public facility as the source.


Your doctor will advise which treatment is right for you. Antibiotics are effective in treating most people with this infection.  


There is no vaccine for Legionnaires' disease. There are many ways to prevent Legionella:

  • Avoid letting water become stagnant by flushing unused taps\showerheads on a weekly basis, by running the cold tap for 2 minutes then doing the same to the hot tap. If it is a singular tap put handle to the cold side and run for 2 minutes, then turn to hot side and run until the water starts to feel hot.
  • Store water at the correct temperature, including hot water heaters (see: Water temperature and burns/scalds - –(this guidance suggests setting tanks to 60°C to prevent growth of Legionella, but to install automatic anti-scald mixing valves on faucets, showers etc. to allow hot water release at 49°C).
  • Devices and equipment that release water in forms of droplet or mist (e.g., humidifiers and misters, medical devices) should be cleaned and maintained regularly as per manufacturers guidelines to prevent growth of legionella. 
  • Proper construction and maintenance of air conditioning and plumbing systems in large buildings and decorative fountains is required to ensure that legionella bacteria do not multiply.
  • If you own a hot tub, disinfection of the water can prevent the growth of legionella that might naturally be present in the water.
    • Make sure there is enough disinfectant in the water prior to using your hot tub.
    • If necessary, add disinfectant at least a half an hour before using the hot tub. 
    • Chlorine levels should be maintained at 3.0 ppm and bromine levels should be maintained at 4.5 ppm. Test kits are available at hot tub and swimming pool stores.

For information about hot tub use and maintenance refer to HealthLink BC Residential hot tub and pools: Safety tips and Residential hot tubs and pools: Safe water quality

SOURCE: Legionnaires Disease and Pontiac Fever ( )
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