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Legionellosis is a disease caused by Legionella pneumophila bacteria. There are 2 clinical forms of legionellosis. The benign form is called “Pontiac fever”. It is characterized by flu-like symptoms of fever and cough. It generally appears 1 to 2 days following exposure to the bacteria. Recovery usually takes 2 to 5 days and most cases do not require treatment.

The most serious form of legionellosis, Legionnaires' disease, is characterized by a lung infection, pneumonia. It generally appears 2 to 10 days following exposure to the bacteria and can be severe, especially in vulnerable individuals.

Legionellosis can occur at any time of the year but is more common in summer and fall. Most cases in Québec are isolated and sporadic. Outbreaks are rare.


The following symptoms may be associated with legionellosis:

  • Fever
  • Headache
  • Fatigue
  • Dry cough or difficulty breathing
  • Muscle pain
  • Loss of appetite
  • Diarrhea, nausea and vomiting
  • Chest pain
  • Bloody sputum
  • Changes in mental state (delirium, confusion, disorientation and hallucinations)


The complications associated with Legionnaires' disease are:

  • Respiratory distress
  • Septic shock, in other words, a sudden drop in blood flow caused by infection with Legionella bacteria
  • Acute renal failure
  • Multiple organ failure

Legionnaires' disease can cause death in 10 to 15% of cases. This percentage may vary depending on several factors, including age, health and the timeliness of treatment.


Most cases are treated successfully with antibiotics.


Legionnaires' disease is contracted by breathing in airborne microdroplets of water contaminated with Legionella bacteria. The disease is not spread from one person to another.

Sources of infection

The bacteria multiply, especially at temperatures ranging between 32°C and 45°C.

While Legionella bacteria are found in natural water sources (lakes, rivers, streams) and in the ground, the main sources of infection are artificial water sources, such as water cooling towers, hot tubs or water heaters.

The main sources of infection are:

  • Hot water distribution systems, such as water heaters and showers
  • Water cooling towers
  • Spas, hot tubs, whirlpools or Jacuzzis
  • Decorative fountains and water features
  • Certain devices and parts of equipment used in healthcare, such as respiratory therapy equipment (including sleep apnea machines such as CPAP and BiPAP machines) or devices used in dental care


There is no vaccine or preventive treatment to protect people from legionellosis. However, the risk of contracting the disease can be reduced by dealing with possible sources of infection.

Here are some recommendations to help prevent legionellosis:

  • At home:
    • Keep the temperature of your water heater at 60°C. At this temperature, Legionella bacteria cannot multiply. However, it is recommended that you install an anti-scald device on the faucet outlet of the shower and bath to lower the water temperature to 49°C. If your water heater has not been on for a few days, let the hot water run for several minutes.
    • Limit the duration of your shower and if the water in your shower becomes lukewarm, close the faucet as quickly as possible so that you do not use up the hot water in your water heater, which could otherwise increase the risk of Legionella bacteria contaminating the water.
    • Some devices produce mist, such as shower heads, hot tubs, spas and humidifiers. Make sure you clean and maintain these devices properly in accordance with the manufacturer’s instructions. Consult a qualified professional when necessary.
    • Do not use tap water in respiratory therapy equipment. Follow the manufacturer’s recommendations for cleaning the device and its tubing.
  • In buildings:

People at risk

Some people are more at risk of having legionellosis:

  • Men
  • People over 50 years old
  • Smokers
  • Heavy drinkers (over 10 drinks per week for women and over 15 drinks per week for men)
  • People with a chronic disease, such as chronic renal failure, a chronic respiratory or heart disease, diabetes or cancer
  • People receiving treatments that weaken their immune system, such as chemotherapy, corticosteroid therapy or other immunosuppressive treatments
  • People who have recently had surgery

Last update: June 5, 2018


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