The cooling towers stood sentinel against the blue September sky as I arrived in London, Ontario last week. They’re easy to miss normally—functional, unremarkable features of the urban landscape. Today, they’re at the center of an unfolding public health investigation that has left six people hospitalized and a community concerned.
“We’re actively investigating six confirmed cases of Legionnaires’ disease in the City of London,” Dr. Alex Summers told me. As the Medical Officer of Health for the Middlesex-London Health Unit, the fatigue in his voice was evident after days of coordinating the public health response. “All cases have been reported since August 26.”
Walking through the affected northeastern neighborhood where most cases have been detected, it’s impossible to tell which cooling system might be harboring the bacteria. Legionella thrives in warm water systems—cooling towers, hot tubs, decorative fountains—places where water can become aerosolized and breathed in by passersby.
Margaret Chen, 67, lives in the area and told me she’s changed her routine. “I’m keeping my windows closed for now, even on these nice days,” she said, adjusting her mask as we spoke on her porch. “My doctor says I’m high risk because of my COPD.”
The health unit is working methodically, sampling water from cooling towers in the northeastern part of the city. Dr. Summers explained they’re prioritizing locations near where patients lived or visited before becoming ill. This methodical detective work is critical—Legionnaires’ disease doesn’t spread person-to-person, but finding the environmental source can prevent more infections.
Most concerning for health officials is that all six patients required hospitalization. Legionnaires’ disease, a severe form of pneumonia, can be particularly dangerous for older adults, smokers, and those with weakened immune systems or chronic lung conditions. Symptoms typically emerge 2-10 days after exposure and include cough, shortness of breath, fever, muscle aches, and headaches.
The disease gets its name from its first documented outbreak—a 1976 American Legion convention in Philadelphia where 182 people fell ill and 29 died. Before the bacterium was identified, the mysterious illness caused considerable alarm. Today, while treatable with antibiotics, Legionnaires’ still requires prompt medical attention.
“We’re seeing about 25 to 30 cases of Legionnaires’ disease annually in Ontario,” said Dr. Emily Wilson, an infectious disease specialist at London Health Sciences Centre not directly involved in the investigation. “Most are sporadic, isolated cases. When we see a cluster like this, it suggests a common environmental source.”
According to Public Health Ontario, Legionnaires’ incidence has gradually increased over the past decade, though improved diagnostic testing may partially explain the rise. The Ontario Building Code now includes specific regulations for cooling tower maintenance to prevent bacterial growth, implemented after a 2005 outbreak in Toronto infected 135 people and killed 23.
Back at the health unit offices, environmental health officers coordinate with building managers to collect samples and review maintenance records. Cooling towers require regular cleaning and chemical treatment to prevent biofilm formation where Legionella and other bacteria can flourish.
“Property managers have been cooperative,” noted Summers. “Everyone understands the urgency.”
While the investigation continues, health officials emphasize that municipal water remains safe. The bacteria must be inhaled in aerosolized droplets to cause infection—drinking water poses no risk. Still, the health unit has advised anyone experiencing symptoms to seek medical attention and mention potential Legionnaires’ exposure.
Outside St. Joseph’s Hospital where several patients are being treated, respiratory therapist Manuel Rodriguez explained the challenge these cases present. “Legionnaires’ can look like many other types of pneumonia initially. That’s why the health unit alert was so important—it puts this possibility on clinicians’ radar.”
For London residents, the outbreak serves as a reminder of the complex infrastructure that supports urban life, and how maintenance of these systems directly impacts public health. As climate change brings warmer temperatures to southern Ontario, creating more favorable conditions for bacteria like Legionella, the importance of vigilant monitoring increases.
Health unit officials expect testing results within days and have promised transparency as the investigation unfolds. In the meantime, cooling tower inspections have expanded to additional buildings in the area.
As evening fell over London, I watched workers in protective gear collecting samples from a rooftop cooling system. This methodical public health response, largely invisible to most residents, represents the front line in preventing what could become a larger outbreak.
“We’ll find the source,” Dr. Summers assured me as we ended our conversation. “These investigations are complex, but the evidence eventually points us in the right direction.”
For now, Margaret and her neighbors wait for answers, windows closed against the invisible threat, reminding us that public health vigilance never truly ends—it just shifts to meet each new challenge.
