The Middlesex-London Health Unit is investigating an outbreak of legionnaires’ disease in the city.
The rare, airborne respiratory illness is due to legionella bacteria, which is usually found in warm water sources such as hot water tanks and air conditioning systems.
Since July 24, 20 cases of legionnaires’ disease have been diagnosed, starting with a business in the south end of London and spreading to a neighbourhood in the southeast. Ten of these cases have resulted in hospitalizations.
“To be clear, 50 per cent of people exposed are hospitalized, or that 50 per cent of people who are infected will be hospitalized, these are people who are already at the most severe cases,” says Dr. Joanne Kearon, associate medical officer of health with the MLHU.
Legionnaires’ disease is not considered contagious from person to person. It can cause high fever, chills and a dry cough, and lead to severe symptoms in older and immunocompromised populations, as well as smokers.
“It’s not very infectious at all; most people exposed will not develop any symptoms,” Kearon says. “Even though it lives in water, it’s not waterborne. It’s not from drinking water, it lives in cooling towers or air conditioning units and then that gets aerosolized or misted into the air and people breathe it in, which is why it becomes a pneumonia.”
Legionella bacteria like warm water, so every year it is common to see sporadic cases, especially in summer. What’s happening this year is an outbreak, where many people have likely already been exposed but will never develop symptoms.
On July 24, the health unit became aware of cases that were in a closer geographic area than normal, and reports came more quickly.
“This is a community outbreak, and the area we’re looking at is southeast London, but it’s quite a large geographic area,” Kearon says. “It’s a five-kilometre radius area that we’re looking at for this investigation, and we’re needing to go out and look for a source in the environment.”
The health unit, along with Public Health Ontario, is broadly looking at potential places of origin, and slowly narrowing down to a smaller area. The MLHU is stressing that there is no risk to the drinking water, as the infection isn’t waterborne.
“If people do become infected, typically their symptoms are mild. It’s what’s called Pontiac’s fever, and those people typically don’t present to the emergency room, don’t test it and so they’ve never identified to us,” Kearon says. “We are seeing legionnaires’ disease, meaning these are people whose symptoms have progressed. They’ve developed a pneumonia, so they have gone to hospital. They’ve been tested and those are the cases that get reported to us.”
The health unit continues its search for the source of the outbreak, and updates will come as they are available.