Legionnaires' disease is a type of pneumonia. The agent that causes Legionnaires' disease is a bacterium called Legionella pneumophilia.
People catch Legionnaires' disease by inhaling small droplets of water suspended in the air, which contain the bacteria.
Conditions that increase the risk from legionella include:
- a suitable temperature for growth, 20°C to 45°C
- a source of nutrients for the organism, such as sludge, scale, rust, algae, and other organic matter
- a way of creating and spreading breathable droplets, such as the aerosol created by a cooling tower or spa pool
Outbreaks of the illness occur from exposure to legionella growing in purpose-built systems where the water is maintained at a temperature high enough to encourage growth. Examples include cooling towers, evaporative condensers, spa pools, and hot water systems used in all sorts of work and domestic premises.
Most community outbreaks in the UK have been linked to installations such as cooling towers, which can spread droplets of water over a wide area. These are found as part of air-conditioning and industrial cooling systems.
To prevent exposure to the legionella bacteria, employers must comply with legislation that requires them to manage, maintain and treat water systems in their premises properly. This will include, but is not to be limited to, appropriate water treatment and cleaning regimes.
The Health and Safety Executive (HSE) has produced an Approved Code of Practice and Guidance on controlling legionella bacteria in water systems to assist employers in assessing the risk of employees and others in the workplace contracting Legionnaires' disease. Copies of the guidance can be obtained from HSE books.
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