Legionnaires’ disease is a potentially fatal form of pneumonia and anyone can be susceptible to infection. The risk of infection increases with age (people over 45 years of age are more at risk) as well as with smokers and heavy drinkers, anyone with an impaired immune system and people suffering with respiratory, kidney, lung or heart disease.
The bacterium Legionella pneumophila and related bacteria, are common in natural water sources such as rivers, lakes and reservoirs, but usually in low numbers. The conditions are rarely right for people to catch the disease from these sources.
Outbreaks of the illness occur from exposure to legionella growing in purpose-built systems where water is maintained at a temperature high enough to encourage growth, such as cooling towers, evaporative condensers, hot and cold water systems and spa pools used in all sorts of premises.
People contract Legionnaires’ disease by inhaling small droplets of water (aerosols), suspended in the air, containing the bacteria. Certain conditions increase the risk from legionella if:
the water temperature in all or some parts of the system may be between 20-45 °C, which is suitable for growth
it is possible for breathable water droplets to be created and dispersed e.g. aerosol created by a cooling tower, or water outlets
water is stored and/or re-circulated e.g. hot and cold water systems
there are deposits that can support bacterial growth providing a source of nutrients for the organism e.g. rust, sludge, scale, organic matter and biofilms