This article is written by Daniel Robert, Senior Vice President, Special Projects, and was published in GESTION IMMOBILIÈRE magazine. To read the full article in the magazine, you can access it via the following link: Gestion immobilière – N°1 – March 2026
Legionnaire’s disease takes its name from a striking episode that occurred in 1976 at an American Legion convention in Philadelphia, where an outbreak of severe pneumonia affected several dozen people. The epidemiological investigation identified a previously unknown bacterium, Legionella pneumophila, associated with a water-cooling system. Since then, numerous sporadic cases and a few outbreaks have been documented around the world, often linked to technical building installations. These events have had a profound influence on operating practices, regulations and the development of technical guides, notably by ASHRAE.
Legionellosis is an infection caused by bacteria of the genus Legionella, naturally present in freshwater. More than 60 species are known, but Legionella pneumophila is responsible for the majority of human infections. There are two main clinical forms: Pontiac fever, a mild flu-like illness, and Legionnaires’ disease, a potentially serious pneumonia. For building managers, this bacterium poses a major environmental problem, as it proliferates in certain hydraulic systems when conditions of temperature, stagnation and nutrients are met.
Legionnaires’ disease generally manifests itself 2 to 10 days after exposure. Symptoms include high fever, dry cough (irritative without sputum) or coughing up secretions from the bronchi, chest pain, shortness of breath, marked fatigue, headaches and muscle aches. Digestive symptoms (diarrhea, nausea) and neurological symptoms (confusion) may also occur. Possible complications include acute respiratory distress, septic shock, renal failure and multivisceral failure. The mortality rate is estimated at between 10 and 15%, particularly in the elderly, smokers and immunocompromised individuals.
Treatment of Legionnaires’ disease is based on rapid administration of appropriate antibiotics (macrolides or fluoroquinolones). Hospital treatment is often required for severe cases. However, there is no vaccine or individual preventive treatment. Prevention therefore relies entirely on mastery of technical installations and proper management of water systems.
Legionellosis is not transmitted from one person to another. Infection occurs through inhalation of micro-droplets of water (aerosols) contaminated with the bacteria. These aerosols can be generated by a variety of equipment: water-cooling towers, showers, spas, decorative fountains or humidifiers. Ingestion of contaminated water is not a significant mode of transmission.
Several sources of infection have been identified:
– Water-cooled cooling towers, including the entire network inside the
The combination of lukewarm water (25 to 45°C), recirculation, the presence of biofilms, nutrients (organic matter, corrosion) and aerosol production make buildings where water circulates a major potential source. Inadequate design of the tower, but also of the network, which may include sections of stagnant water, inadequate maintenance, ineffective water treatment or prolonged stoppages, significantly increase the risk of contamination. The location of fresh air intakes close to the towers can also encourage the spread of airborne pathogens.
inside buildings.
– Domestic hot water systems are an often underutilized source of energy.
estimated. Water heaters, recirculation loops, showers and little-used pipe sections can promote stagnation and maintain temperatures ideal for bacterial proliferation. Water and energy-saving strategies, if poorly integrated into the design, can accentuate these risks.
The prevention of legionellosis is based on a proactive, systemic approach. Key measures include
- Maintain proper temperatures (≥ 60 °C (140 °F) at the water heater, ≥ 55
- C (130°F) in the loops, with anti-scald devices at points of use).
- Eliminate stagnation through proper hydraulic design (dead-leg reduction, loop balancing).
- Implement a rigorous water treatment program for cooling towers (biocides, pH control, corrosion and scaling).
- Considering a tower water filtration system can also be an effective method of reducing nutrient sources that favor bacterial growth.
- Clean and disinfect systems on commissioning, after extended shutdowns or according to a set schedule.
- Ensure that towers are equipped with drip shields in good condition to minimize spread in the event of an outbreak.
- Keep detailed records of operations, maintenance, analyses and interventions.
- Train personnel and use appropriate personal protective equipment during hazardous operations.
ASHRAE adopts a risk management approach. ANSI / ASHRAE 188-2021 establishes minimum requirements for managing the risk of Legionella in building water systems. It requires the development and implementation of a water management program identifying hazards, control points, operational limits and corrective actions. In addition, ASHRAE Guideline 12-2023 provides practical recommendations specific to different systems (drinking water, cooling towers, fountains, spas). ASHRAE emphasizes the responsibility of owners and operators in prevention, rather than a purely reactive approach after an outbreak.
In Quebec, the Régie du bâtiment du Québec (RBQ) strictly supervises water cooling tower installations. The Règlement sur l’entretien d’une installation de tours de refroidissement à l’eau, integrated into the Safety Code, has been in force since 2014. In particular, it requires:
- the obligation for the owner to declare all installations to the RBQ upon commissioning and on an annual basis;
- drawing up a maintenance program to maintain water quality, signed by qualified professionals;
- regular water analyses by recognized laboratories;
- keeping registers accessible to the authorities ;
- safe shutdown of plants during extended shutdowns.
These requirements make building managers key players in public health. Rigorous, documented operation that complies with technical and regulatory guidelines is now essential to reduce the risk of Legionnaires’ disease over the long term.
Beyond prevention, any serious organization should draw up a response plan in the event of tower contamination. This plan, often consisting of several stages, is applicable according to established contamination thresholds.
Before the warm season arrives, it’s a good idea to take a closer look!
Note: An engineer by training, Daniel Robert is Senior Vice President, Special Projects at Kolostat Inc. An influential member of ASHRAE, the global reference for HVAC technologies, he served on the Chapter’s Technology Transfer Committee (CTTC) in 2022-2023, and was President of the Montreal Chapter in 1992.
References:
– Article from Gestion immobilière ; Gestion immobilière – N°1 – March 2026