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Managing the risk of Legionella in water supply networks has been required in all public buildings (établissements recevant du public, ERP) since 2010, 2011 or 2012, depending on the category (ministerial statement of February 1, 2010). The establishments that are subject to these regulations are those with facilities that present a risk of bacterial proliferation and aerosolization of contaminated water, including:
• connection to the public hot water supply (eau chaude sanitaire, ECS) with points of use that could spread contamination: showers, shower heads, taps, etc. Bacteria can be dispersed over a distance of several meters.
• whirlpool baths and all leisure, care or well-being activities associated with water. Dispersion can cover several dozen meters.
• cooling towers (tours aéroréfrigérantes, TAR) that cool water via evaporation and other cooling facilities that cool water by dispersion in the air flow. Dispersion can cover several hundreds of meters, or up to several kilometers. Learn more
Bacteria from the genus Legionella sp. are normally present in the environment, particularly in aquatic environments. These bacteria easily colonize water-based facilities, which provide favorable growing conditions:
• stagnant water or water that only circulates occasionally (for example, seasonal facilities);
• temperatures between 25 and 45°C (the optimum temperature is 32-35°C);
• trace elements (iron, zinc);
• biological contamination of the network by biofilms or protozoa.
These germs proliferate preferentially in hot water (eau chaude sanitaire, ECS) networks that are not monitored for microbiological contamination, especially in zones where water is routinely maintained at lukewarm temperatures. Completely eradicating these germs is difficult due to their extreme resistance to disinfecting agents.
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Airborne transmission of Legionella occurs via the inhalation of microdroplets of contaminated water (aerosols). Infection can cause:
• benign illness with flu-like symptoms (Pontiac fever);
• serious illness with severe pneumonia (legionellosis), which can cause death in vulnerable individuals (15% of cases). Legionellosis is therefore a reportable disease.
The severity of the infection depends on the number of micro-organisms inhaled, the virulence of the strain and the immune status of the infected individual. Legionella pneumophila serogroup 1 is by far the most common strain.
Legionella resistance to biocidal disinfection agents (sometimes up to 50 mg/L of chlorine) and thermal shock (sometimes up to 70°C) depends strictly on the presence of the following elements in water supply networks:
• biofilms that provide a preferred ecological niche for Legionella. They can establish colonies in biofilms and proliferate within their protective organic matrices. Learn more
• planktonic micro-organisms (including multiple protozoan species: Naegleria, Acanthamoeba, Tetrahymena), in which Legionella can reside and multiply in the form of intracellular cysts.
For this reason, effective prevention relies not only on eliminating free Legionella bacteria, but also on eradicating biofilms and planktonic protozoa.
➟ Learn more about our rapid microbiological analysis solutions for analyzing and monitoring risks within water supply networks and evaluating disinfection processes.