Legionella bacteria can be found in any freshwater environment, such as rivers and lakes. The bacteria are usually only present in low numbers because the temperature of the water is often too low for the bacteria to grow and spread.
However, if the bacteria manage to find their way into an artificial water system, given the right circumstances, they can quickly grow and reproduce, leading to a widespread contamination of the water system.
The two things that the legionella bacteria require to grow and reproduce are:
- a water temperature of between 20-45ºC (68-113ºF)
- impurities in the water that the bacteria can use for food, such as rust, sludge, algae and limescale
Water systems that are known to be vulnerable to legionella contamination include:
- hot and cold water systems for large buildings, such as hotels and hospitals
- air conditioning systems that use water for cooling purposes
- cooling towers
However, any artificial water system is potentially vulnerable to contamination. For example, cases of Legionnaires’ disease have reportedly arisen from contaminated:
- baths and showers
- fountains
- sprinkler systems
- whirlpool baths
- spas
- humidifiers that were being used in food display cabinets
You can catch Legionnaire’s disease by drinking contaminated water or by inhaling small droplets of contaminated water mist in the air.
Risk factors
Everyone is potentially at risk of developing Legionnaires’ disease. However, a number of risk factors make it more likely for certain individuals to experience a more severe form of the infection. These risk factors include:
- being 50 years of age or over
- being a smoker or having a past history of heavy smoking
- having diabetes
- having kidney disease
- having a weakened immune system (the body’s natural defence against infection and illness) – for example, people with HIV and AIDS
- having cancer, particularly lung cancer or leukaemia (cancer of the white blood cells)
- having a pre-existing lung condition, such as chronic obstructive pulmonary disease
- having a heart condition, such as heart failure
- having a liver condition, such as alcoholic liver disease
