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Cases of Legionnaires' disease in Montréal: Public Health Investigation

Update : October 4, 2018

Since last August 22, no new cases of Legionnaires' disease have been reported to Montréal's regional public health department, in connection with the four cases for which a common environmental source of the Legionella bacteria had been suspected. The investigation did not identify a common source of exposure to the Legionella bacteria. Public health continues to investigate all reported cases of Legionnaires' disease. 

Update : September 4, 2018

Cases of Legionnaires' disease in Montréal: The Public Health Investigation Is Ongoing

Since August 22, the public health department has not received any reports of new cases of Legionnaires’ disease related to the four cases who may have contracted the illness from the same source of the Legionella bacteria.

On Wednesday, August 29, the director of public health issued a preventive decontamination order to all owners of cooling towers located in the targeted area. Immediately upon reception of the order, the owners are under an obligation to decontaminate their towers.


The Direction régionale de santé publique de Montréal (DRSP) investigates all reports of Legionnaires' disease cases it receives. Currently, four residents living in the north part of the island, south of the Metropolitan in the city’s Anjou borough, may have contracted the illness through the same environmental source. The investigation aims to determine if the cases are linked, and to identify and eliminate the source of exposure. 

No outbreak of Legionnaires' disease or increase in the number of cases has been confirmed in Montréal. Each year in Montréal, about 40 people contract the disease. However, the DRSP has contacted the health network, asking workers to be vigilant and report all new cases of Legionnaires' disease. 

Public health is not recommending that people change their lifestyle habits or destinations. 

What is Legionnaires' disease? 

Legionnaires' disease does not occur frequently in Québec, and the risk of contracting it remains low for people in good health. It is caused by a bacteria called Legionella. Most of the time, the disease causes a lung infection (pneumonia) that is treated with antibiotics. The Legionella bacteria is widespread in the environment (natural or artificial water). 

Legionnaires' disease does not spread from person to people. It is contracted by inhaling (breathing in) tiny droplets of water contaminated with large quantities of Legionella bacteria spread into the air (aerosols) by water-cooling towers, hot water distribution systems (e.g. hot-water heaters), water fountains, spas, etc. You can’t get it by drinking contaminated water. Illness occurs 2 to 10 days after a person has been exposed to and infected with the Legionella bacteria. 

Epidemiological investigation underway 

The DRSP, in collaboration with Régie du bâtiment du Québec (RBQ), is checking for the presence of the bacteria in cooling towers within 3 km of the area of the reported cases. Since 2014, a regulation has required owners of cooling towers to keep their towers properly maintained and monitor them for bacteria. Public health teams are also investigating other possible sources of contamination, for instance, the cases’ homes (hot-water heater) or travel in the area. 

Who is most at risk of getting the disease? 

Overall, Legionnaires' disease does not present a danger for people in good health. However, some people are at higher risk: people 50 years of age or older, men, people with chronic diseases (e.g. diabetes, respiratory disease, heart disease) or weak immune systems (e.g. cancer, transplant, etc.), smokers and people who drink a lot of alcohol. 

What are the symptoms? 

Legionnaires' disease can cause a variety of symptoms. Some of the most common are fever, chills, cough and difficulty breathing. Other symptoms can also develop, such as headaches, muscle pain and digestive problems (e.g. loss of appetite, nausea, vomiting or diarrhoea). 

What to do if you have these symptoms? 

If you have persistent fever and difficulty breathing, call Info-Santé at 8-1-1 or see a doctor quickly. For more information.

Source: Direction régionale de santé publique de Montréal
Information: Relations médias du CIUSSS du Centre-Sud-de-l’Île-de-Montréal
Media line: 514-376-3748 Email: 

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