Warming temperatures are leading to a rise in this deadly disease
An increase in cases of Legionnaires’ disease around the world can be attributed to warming temperatures from climate change.
Average temperatures are on the rise around the world as our climate continues to change at an unnatural rate, a fact that also comes with the rising threat of deadly diseases.
Scorching summer temperatures and frequent heatwaves have increased the demand for efficient cooling systems in homes and buildings, as well as the demand for water sources to help beat the heat. This increased demand to beat the heat, however, comes with its own serious risk: Legionnaires’ disease.
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What is Legionnaires’ disease
Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria, which loves to grow in warm water. While the bacteria can be found naturally in fresh water, it only poses a threat to human health when it is in a human-made water system, such as pipes and hoses, where it can quickly grow into dangerous concentrations.
You cannot catch Legionnaires’ disease from another person. Instead, it spreads when someone inhales mist or water contaminated with the bacteria.
The deadly disease got its name after an outbreak in 1976 at an American Legion convention in Philadelphia. The event, which cost 28 lives, was also how the Legionella bacteria was first discovered.
Additionally, the number of confirmed cases has been increasing each year over the past couple of decades in Canada and the United States.
We are seeing an upward trend in cases of Legionnaires' disease in Canada since 2004. (Government of Canada)
Recent outbreaks
After a long period of hot weather in Eastern Canada and the United States, New York City saw one of its largest Legionnaires’ disease outbreaks in years in mid-August, 2025. According to USA Today, the culprits behind the outbreak were the cooling towers on a group of large buildings in Harlem, a neighbourhood in Manhattan.
Cooling towers are used to remove excess heat from large-scale air cooling systems that use cold water to lower temperatures. When not properly maintained, Legionella bacteria can grow in the water lines. When the towers release mist from the excess heat, they can spread the bacteria to people nearby. Those who unknowingly inhaled the contaminated mist then became at risk of developing Legionnaires’ disease.
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Closer to home, a meat-processing plant in London, Ont., also fell victim to an outbreak in July and August of 2025 due to improper maintenance of the plant’s cooling towers.
Poor maintenance of water pipes can allow Legionella bacteria to grow, increasing the risk of Legionnaires' disease. (U.S. Centers for Disease Control and Prevention)
We could see more future outbreaks thanks to climate change
As temperatures in North America continue to rise due to global climate change, it’s likely we’ll see a rise in the number of Legionnaires’ outbreaks as our reliance on cooling systems and towers increases. The systems will also have to work harder and longer to offset the intensifying and prolonged summer heat.
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It’s not just large-scale cooling systems that can spread Legionella bacteria, however. Hoses and pipes from everyday fixtures, such as water fountains, pools, and garden hoses, can also become a breeding ground for the bacteria when exposed to the heat.
Additionally, warmer temperatures in lakes and ponds can help the bacteria grow above safe levels, posing a risk to swimmers looking to cool off.
Properly maintaining water systems will become even more important going forward as we see average air temperatures in Canada and around the world continue to rise, not just for cooling off but also for our health.
Thumbnail image taken by Connor O'Donovan/TWN
