Legionellosis is a serious lung infection caused by bacteria of the genus Legionella. It is contracted by inhaling fine droplets of contaminated water suspended in the air — not by drinking the water — and it does not pass from person to person.
Where the bacterium grows
- Domestic hot water networks held at intermediate temperatures.
- Cooling towers and cooling circuits.
- Whirlpool baths, showers and misting systems.
- Any pipework where water stagnates and biofilm takes hold.
The temperature range between roughly 20 and 45 °C is particularly favourable to it. Above 60 °C, the bacterium does not survive.
The symptoms
High fever, cough, muscle pain, headaches and sometimes digestive upset. Incubation generally lasts from two to ten days. Older people, smokers and the immunocompromised are the most exposed. A prompt medical diagnosis is decisive.
Prevention
It rests on principles that are simple but demanding: keep hot water above 55 to 60 °C as it leaves production and cold water below 20 °C, remove dead legs, regularly flush little-used outlets, maintain the cylinders and monitor at-risk installations.
In a hotel, a healthcare facility or an industrial site, this monitoring belongs in a written, documented plan, not an occasional check.