Legionnaires Disease, Symptoms, Outbreak and Prevention: What You Need to Know

According to recent reports, Ontario witnessed a sudden Legionnaires disease outbreak in Ontario, with more than 12 cases already reported that are locally clustered. However, healthcare providers agree that even though legionella bacteria and common legionella pneumonia remains a serious concern, it is still a preventable form of pneumonia, and understanding the basics for this disease is essential for legionnaires disease prevention. In this blog we will try to delve deep into legionella symptoms, legionella pneumonia, legionnaires disease prevention and what we can collectively or individually do to stop legionella bacteria in water from growing.

Understanding Legionnaires Disease and Legionella Bacteria

Legionnaires disease or legionella pneumonia is a severe lung infection caused by legionella bacteria, most often Legionella pneumophila. These bacteria thrive in warm, stagnant water. Because they spread through inhaled droplets, they pose a risk wherever water systems create mist or aerosol.
Health Canada explains that Legionella bacteria exists naturally in freshwater but becomes dangerous when it multiplies in manmade systems such as cooling towers, HVAC systems, hot tubs, decorative fountains, and large plumbing networks. Although most people exposed do not get sick, those who do can develop lifethreatening pneumonia.
Because legionella pneumonia spreads only through water droplets and not persontoperson contact, prevention focuses on water system safety rather than isolation or respiratory precautions.

How Legionella in Water Leads to Common Legionella Pneumonia

Legionella bacteria grows best in warm water between 20°C and 50°C. When conditions allow it to multiply, the bacteria can enter building systems and spread through mist. As a result, legionella in water becomes the primary source of common legionella pneumonia.
Legionella in water can grow in made systems such as cooling towers, hot tubs, decorative fountains, and large plumbing networks. Although most people exposed do not get sick, those who do can develop lifethreatening pneumonia.
Because Legionella spreads only through water droplets and not person-to-person contact, prevention focuses on water system safety rather than isolation or respiratory precautions.

How Legionella in Water Leads to Common Legionella Pneumonia

Legionella grows best in warm water between 20°C and 50°C. When conditions allow it to multiply, the bacteria can enter building systems and spread through mist. As a result, legionella in water becomes the primary source of common legionella pneumonia.
Public Health Ontario notes that people inhale contaminated droplets from showers, humidifiers, cooling towers, HVAC systems, or even grocery stores. Because the lungs receive these droplets directly, the bacteria can settle deep in the respiratory tract and cause the infection.
Although Legionella does not spread through drinking water, swallowing water “down the wrong pipe” can also cause infection in rare cases.

Legionella Symptoms: What to Watch For

Recognizing legionella symptoms early helps reduce complications. Symptoms usually appear 2–10 days after exposure, although some cases take longer.
Common legionella symptoms include:

• Fever
• Cough
• Shortness of breath
• Muscle aches
• Headache
• Gastrointestinal upset
• Confusion in severe cases

It is important to note that these symptoms resemble other pneumonias. However, Legionnaires disease often progresses faster. Because of this, Health Canada recommends immediate medical attention when symptoms appear after exposure to aerosolized water sources.

Legionnaires Disease Outbreak Patterns in Canada

A legionnaires disease outbreak occurs when two or more cases link to the same water source. Outbreaks often involve cooling towers, HVACs, large plumbing systems, or industrial water systems. Because the lungs receive these droplets directly, the bacteria can settle deep in the respiratory tract and cause infection.
On an average, Canada reports about 100 documented legionnaires disease cases every year. However, the actual number may be higher. This is because a number of people usually mistake them for regular pneumonia and do take a legionella bacteria test.
Because Legionella thrives in warm weather, outbreaks often appear in late summer or early fall.

History of Legionnaires Disease Outbreak in Canada

Quebec witnessed a significant legionnaires disease outbreak in 2012, when 13 deaths and 170 documented cases were reported in the province from a cooling tower in a building. Likewise, Calgary reported eight cases of this disease in the same year from a construction site water spray.

Recent Legionnaires Disease Outbreak Examples

Cases continue to rise, as Ontario reported 354 cases and 26 deaths in 2024, and the province also confirmed multiple outbreaks in both 2025 and 2026. CTV News reported a Toronto outbreak where public health officials confirmed multiple cases linked to a localized water source. Additionally, Hamilton also reported a “cluster” of 13 confirmed legionellosis cases last week in the city’s east end and in Stoney Creek.

Public health teams usually investigate by:

• Testing water systems
• Reviewing building maintenance logs
• Sampling cooling towers
• Issuing public advisories
• Recommending immediate disinfection

Although outbreaks are rare, they require rapid action because Legionnaires disease can cause severe illness, especially in vulnerable groups.

Is There a Chance of a Legionnaires Disease Outbreak in Winnipeg?

Winnipeg’s climate reduces Legionella growth during winter, yet the risk does not disappear. In 2016, a cancer unit at the Victoria General Hospital detected Legionella bacteria, but officials assessed the risk to patients as low and did not declare an outbreak. Because Legionella thrives in warm, stagnant water, any building with complex water systems can experience bacterial growth if maintenance lapses.

Winnipeg-Specific Risk Factors

Winnipeg buildings with the following features carry higher risk:

• Cooling towers in commercial buildings
• Large apartment or condo plumbing systems
• Hospitals and longterm care facilities
• Industrial water systems
• Hot tubs and spas

Although Winnipeg has not reported a major outbreak recently, the possibility exists because Legionella appears in water systems across Canada. Public health agencies emphasize that prevention depends on maintenance rather than climate alone.

Legionnaires Disease Prevention and Water System Safety

Health Canada, the National Research Council of Canada, the Public Health Agency of Canada, Public Services and Procurement Canada, and the Treasury Board of Canada Secretariat all play active roles in reducing the risks associated with Legionellarelated disease outbreaks. These federal bodies share guidelines that help organizations, construction companies, and individuals manage water systems safely and prevent Legionella growth.
Effective legionnaires disease prevention focuses on controlling legionella in water. Because Legionella grows in warm, stagnant environments, prevention requires consistent monitoring. Additionally, we must also note that Legionella does not spread person-to-person. Hence, prevention primarily should focus on water safety.

Key Prevention Steps for Buildings

Health Canada and Public Health Ontario recommend:

• Maintaining hot water at 60°C at the tank
• Keeping cold water below 20°C
• Flushing rarely used taps
• Cleaning and disinfecting cooling towers
• Using biocides where appropriate
• Monitoring water temperature and chlorine levels
• Preventing scale and sediment buildup

These steps reduce bacterial growth and prevent aerosolized spread.

Prevention Tips for Homeowners

Although most outbreaks involve large systems, homeowners can still reduce risk by:

• Flushing taps after vacations
• Cleaning showerheads
• Maintaining hot water tanks
• Avoiding stagnant water in humidifiers
• Replacing filters regularly
• Follow the guidelines from the National Building Code of Canada (NBC). For example, specifies that coolingtower blowdown products must remain a minimum distance from outdoor air intakes and connect directly to the building’s drainage system. It further includes measures that prevent warm discharge air and drift from entering indoor spaces, mitigate the growth and spread of Legionella, protect potable water sources, and ensure that evaporative equipment has proper service platforms.

Medications Available for Legionella Bacteria

Clinicians use azithromycin, doxycycline, or levofloxacin as firstline antibiotics to treat legionnaires disease and common Legionella pneumonia. However, they can also recommend fluoroquinolones for severe cases. All of them are prescription medications and are not available over the counter.

Here’s the Breakdown of Antibiotics Clinicians Use to Address Legionella Symptoms:

• Azithromycin — prescriptiononly macrolide antibiotic
• Doxycycline — prescriptiononly tetracycline antibiotic
• Levofloxacin — prescriptiononly fluoroquinolone antibiotic.

Because these medications treat serious infections, clinicians must assess symptoms, confirm the diagnosis, and choose the safest option based on age, kidney function, other medications, and the severity of legionella symptoms.
The medications mentioned above usually treat immunocompetent patients for 10–14 days. However, doctors may also extend therapy to 21 days for immunocompromised patients, since legionella bacteria can cause more persistent illness in vulnerable groups. Nevertheless, with timely and appropriate antibiotics, clinicians usually resolve 95–99% of the legionella symptoms.

Who Is Most Vulnerable to Legionnaires Disease?

Although anyone can get Legionnaires disease, certain groups face higher risk. According to Health Canada, vulnerable populations include:

• Adults over 50
• Smokers
• People with chronic lung disease
• Individuals with weakened immune systems
• People with diabetes, kidney disease, or cancer
• Residents of longterm care homes

Because these groups experience more severe symptoms, early detection and rapid treatment remain essential.

How Health Canada Responds to Legionnaires Disease

Health Canada provides national guidance on Legionella management, outbreak response, and laboratory testing. Their recommendations include:

• Rapid case identification
• Environmental testing
• Coordinated public health investigation
• Communication with building owners
• Immediate remediation of contaminated systems

The Public Health Agency of Canada also maintains pathogen safety data sheets for Legionella pneumophila, outlining laboratory risks and biosafety requirements.

Why Legionnaires Disease Awareness Matters

Although Legionnaires disease remains uncommon in Winnipeg, outbreaks can cause severe illness. Because Legionella bacteria thrives in water systems across Canada, awareness helps communities prevent infections before they occur.

Transitioning to stronger prevention practices protects vulnerable populations and reduces the likelihood of outbreaks in cities like Winnipeg. As buildings age and water systems become more complex, proactive maintenance becomes even more important.

In conclusion, legionnaires disease is preventable, yet it requires consistent attention to water system safety. With proper maintenance, early detection, and strong public health response, communities can stay safe and prevent future outbreaks of Legionnaires disease. If you belong to a vulnerable group, speak to us for more guidance, or book an appointment with our doctors at Express Medical Care.