Public Health Is Investigating A Cluster Of Legionnaires' Disease Cases In Montreal

Montreal public health has launched an investigation after finding 10 cases of Legionnaires' disease in the city in the past 10 weeks, which led to two deaths.

Montreal's Direction régionale de santé publique (DRSP) began receiving reports of Legionnaires' disease cases on June 30, according to a memo shared with MTL Blog.

All cases, including both deaths, were concentrated in a "limited area" in the east end of Montreal, in Rosemont–La Petite-Patrie and Mercier–Hochelaga-Maisonneuve.

Of the 10 cases reported, six were found in men and four were found in women. The average age of people with cases was 71 years old, and 90% of cases were found in people 50 years or older.

Seventy percent of the identified cases were found in immunocompromised patients, and each of the 10 patients was hospitalized due to the illness.

Montreal public health trying to identify the source of new cases

Public health has not yet identified a common source of the cases, but it is not excluding the possibility of "a common environmental source," said Annie Dufour, media relations advisor for the CIUSSS du Centre-Sud-de-l'Île-de-Montréal, in an email.

The Legionella bacteria that cause the disease can be found almost anywhere in the environment — mainly in freshwater, like lakes and rivers, but sometimes in significant quantities of artificial water sources like water cooling towers and water heaters. The bacteria also multiply in warm water, according to information provided by Montreal public health.

Legionellosis is transmitted by fine contaminated microdroplets that can travel long distances in the air — however, the chances of contracting the disease are very low since it isn't transmitted from person to person, Dufour said.

Symptoms of Legionnaires' disease are similar to COVID-19 and include high fever, chills, cough, fatigue, muscle pain and loss of appetite.

Dufour said the DRSP received 45 reports of the disease in 2020, but cases may have been underreported due to COVID-19. As of August 4, the DRSP has received 21 reports of the disease, comparable to 2019 for the same time period.