Legionella in Ontario: A Call for Stronger Regulations

In 2025, Ontario was shaken by a serious outbreak of Legionnaires’ disease, caused by the bacterium Legionella pneumophila.

This bacterium thrives in stagnant water and poorly maintained systems (cooling towers, plumbing networks, fountains, spas). When inhaled as microdroplets, it can cause a severe lung infection, similar to pneumonia, that can be fatal for vulnerable individuals.

In London, Ontario, the contamination was traced back to the cooling towers of a food processing plant. The toll was heavy: 94 cases, 86 hospitalizations, and 4 deaths (CBC News, 2025).

Lab tests confirmed that the strain of Legionella found in patients matched the one present in the cooling towers. Despite a cleaning program in place, the bacteria thrived thanks to ideal conditions—heat, humidity, and water stagnation—that allowed recolonization of the system.

Quebec vs. Ontario: Two Approaches, Two Outcomes

Since 2014, Quebec has enforced strict regulations (Gazette officielle du Québec, 2014) on the maintenance of cooling towers, requiring:

• Mandatory record keeping
• Regular water testing
• Annual cleaning and disinfection

Ontario, on the other hand, has no such framework. Cleaning and monitoring are largely left up to internal company policies (PubMed Central, 2024).

This regulatory gap clearly shows how important a strong framework is to protect public health.

The Pillars of Prevention

To prevent such outbreaks, several measures are critical when managing high-risk water systems:

1. Water Management Plan

   1. A structured program for monitoring, cleaning, and disinfection (canadianwatercompliance.ca, Canada.ca).
   2. Detailed logs of inspections, test results, and corrective actions (canadianwatercompliance.ca).

2. Microbiological Monitoring

   1. Regular testing (culture, PCR) to detect Legionella (Canada.ca, canadianwatercompliance.ca).
   2. Immediate interventions if thresholds are exceeded.

3. Cleaning and Disinfection

   1. Strict protocols with appropriate biocides (chlorine, monochloramine, copper-silver ionization, UV) (canadianwatercompliance.ca, tpsgc-pwgsc.gc.ca).
   2. Cleaners and descalers to remove biofilm and protective deposits (Global News, canadianwatercompliance.ca).

4. Control of Favourable Conditions

   1. Keep hot water above 60 °C to destroy the bacteria (Wikipedia, Canada.ca).
   2. Prevent stagnation through proper circulation and flushing of unused lines (tpsgc-pwgsc.gc.ca, Canada.ca).

5. Training and Procedures

   1. Raising awareness among staff about Legionella risks and proper use of protective equipment (Canada.ca, Ontario).
   2. Written procedures reviewed annually (tpsgc-pwgsc.gc.ca, Ontario).

The Key Role of Chemicals

Cleaning and sanitation product manufacturers play a frontline role:

• Specialized biocides: oxidizing (chlorine, chlorine dioxide) and non-oxidizing (isothiazolinone), adapted to each system (canadianwatercompliance.ca).
• Cleaners and descalers: essential to break down the biofilm that shields the bacteria (canadianwatercompliance.ca).
• Continuous treatment programs: alternating products to prevent microbial resistance, carefully tracking concentrations, and adjusting based on test results (canadianwatercompliance.ca).

In Summary

This outbreak proves a simple truth: one-off cleaning is not enough.

Only a combination of regular monitoring, strict protocols, and strong regulations can truly prevent the spread of Legionella.

In Quebec, regulations enforce these best practices. In Ontario, this tragedy may well serve as a wake-up call to revisit the legal framework.

Constant’s Expertise

At Constant, we know that rigorous protocols make all the difference. We support our clients with:

• Tailored disinfectants and cleaning products
• Validated treatment protocols
• Hands-on technical support to implement effective water management programs

Because beyond compliance, the ultimate goal is to save lives.