Outbreaks of Legionnaires’ disease are not very common, infectious diseases specialist Dr. Isaac Bogoch told CityNews on Tuesday, but even more uncommon is an entire intersection being flagged as a hotspot for possible exposure.
On Monday, Toronto Public Health (TPH) issued a release saying there have been six confirmed cases among people who either live, work, or have visited an approximately one-kilometre radius of the intersection of Bathurst and Dupont streets.
The individuals became symptomatic between Thursday, July 2 and Sunday, July 26.
TPH says it is looking into a possible connection to another recent outbreak in the area, at Castleview Wychwood Towers — a long-term care home where five people contracted the disease as recently as Sunday, July 19, 2026.
But so far, the source of the latest outbreak remains a mystery, leading TPH to flag the entire area.
Does that mean just being in the area could pose a health risk? While outdoor contamination is possible, Bogoch says it’s rare.
“I think it would be less common in an outdoor setting, although of course it can happen, the bacteria lives in water and specifically it lives in amoebas in water, and if the water is aerosolized and people breathe it in (they can get it) if they are prone to infection.”
Most often, there’s an identifiable source.
“This is a bacterial infection and people will acquire this infection from breathing in the bacteria, usually from either nature or a human-made source and the most common human-made sources are from HVAC systems, cooling towers, other air conditioning systems where contaminated water is aerosolized and people breathe it in.
“It’s almost never transmitted from human-to-human,” he stressed. “Almost all cases are from inhaling it from an environmental or human-made source.”
Bogoch also stresses that not everyone that comes into contact with the bacteria will get sick.
“This is one of those infections where multiple people can be exposed but few will actually get the infection, but it can cause pneumonia and a pretty severe type of pneumonia.”
“We don’t see it all that often but we absolutely still see it and they (patients) are overwhelmingly in hospital and sometimes even in the intensive care unit.”
It’s also often difficult for medical professionals to identify Legionnaires’ disease, he adds.
“It’s indistinguishable from other types of pneumonia with fever, cough, shortness of breath.”
He says for anyone with those symptoms, “the list of possibilities is long” and most doctors will prescribe an antibiotic that can address a wide range of illnesses.
“When we look at empiric treatment we don’t often always know what the type of pneumonia it is when we are treating it … and we often cover broadly to cover many different types of infectious pneumonia and usually the antibiotics that we choose will cover Legionella pneumonia because we’re not going to wait for a diagnostic test to come back.”
As far as the source of the recent outbreak, Bogoch says it’s too soon to pinpoint, but in his experience there’s often a short-list of usual suspects.
“It’s always tough to know but when we look at outbreaks of Legionella … they tend to be in cooling towers, HVAC systems, buildings, anything involving water and aerosolization of water, typically in indoor settings, but of course not exclusively.”
TPH says it’s making progress towards identifying the source.
“Possible sources of Legionella bacteria have been identified and are being investigated,” it wrote. “Environmental testing is underway to determine whether the cases can be linked to a common source. At this time, no source of infection has been confirmed and the investigation is ongoing.”
People most at risk of contracting Legionnaires’ disease include people over the age of 50, people who smoke or have chronic diseases and compromised immune systems.
“‘Legionnaires’ disease is more common in men than women and is rare in children and young adults,” TPH adds.
TPH offers the following advice to protect yourself from exposure:
