Montreal

Montreal health authorities ask doctors to look out for legionnaires' disease after scattered cases emerge

Montreal's public health department is asking doctors to look out for instances of legionnaires' disease after seven cases were discovered in southwest Montreal over the last six weeks.

Disease has commonalities with COVID-19; some cases may have gone undiagnosed

This 2009 colorized 8000X electron micrograph image provided by the Centers for Disease Control and Prevention shows a large grouping of Gram-negative Legionella pneumophila bacteria. (Janice Haney Carr/Centers for Disease Control/Associated Press)

Montreal's public health department is asking doctors to look out for instances of legionnaires' disease after seven cases were discovered in southwest Montreal over the last six weeks.

Like COVID-19, legionnaire's disease can cause pneumonia, which has led health officials to believe that some cases may have gone undiagnosed in recent months as the health-care system focused on the novel coronavirus.

An investigation into the seven cases did not reveal any links between them or a common source. Dr. Geneviève Cadieux, a consulting doctor in the public health department's infectious disease prevention division, said a common source — such as a water cooling tower — would typically mean infections closer together geographically and clustered over a shorter time period.

"In this case, with the fact that the cases are far apart in time and space, our suspicion of a common source is lower," she said. "I would say the probability is less. But out of prudence, we still try to ensure that there is not a potential source common to all these cases."

The hypothesis that an overlap of characteristics with COVID-19 may have led to fewer diagnoses is further supported by the fact that there have only been 14 cases of legionnaire's disease since the start of the year in Montreal. In 2019, there were 56 cases detected.

The public health department is asking doctors to consider a legionnaire's disease diagnosis for all patients hospitalized with pneumonia, and especially those where certain other factors, such as diabetes or chronic heart, lung or kidney disease, are present.

Legionnaires' disease got its name from the unfortunate delegates who became infected during an outbreak at an American Legion of Pennsylvania convention. Thirty-four people died. The bacteria responsible for the disease was isolated and named Legionella pneumophila in 1976.

Legionnaires' disease is one of two distinct illnesses associated with the Legionella genus. Its milder counterpart, Pontiac fever, is a non-pneumonia flu-like illness that is less common. People affected by the fever usually don't need treatment and are able to recover within a few days.

With files from Radio-Canada

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