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Legionella and Legionnaires disease

What is legionella?

Legionellosis is a collective term for diseases caused by legionella bacteria including the most serious Legionnaires’ disease. Legionnaires’ disease is a potentially fatal form of pneumonia and everyone is susceptible to infection. The risk increases with age but there are some people who are at a higher risk including:

  • People aged 45 and over
  • Heavy drinkers and smokers
  • People suffering with chronic respiratory or kidney disease
  • People suffering with diabetes, lung and heart disease
  • Anyone with an impaired immune system

Where does it come from?

Legionella bacteria is widespread in natural water sources such as rivers, lakes and reservoirs. However, it is very rare the conditions are 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. 

How do people get it?

Legionella is contracted by inhaling small droplets of water, suspended in the air which contains the bacteria. Certain conditions increase the risk from legionella if your water system:

  • has a temperature between 20-45 degrees Celsius
  • Can create and disperse breathable water droplets, e.g. aerosol created by cooling tower, or water outlets
  • Stores and/or re-circulates water
  • Is likely to contain a source of nutrients for the organisms to grow, e.g sludge, rust, scale, organic matter and biofilms

There are also a number of other potential risk systems that can pose a risk of exposure to legionella, e.g. air washers, emergency showers, humidifiers, indoor ornamental fountains, etc.

Who should be aware of the need to test for legionella?

If you are an employer, landlord or someone in control of a premise, you have a duty to understand and manage legionella risks. All systems require a risk assessment although not all systems will require control measures. A risk assessment may show that the risk of legionella is low and if managed properly will comply with the law. With such cases, an assessment must be complete, you may not have to take further action, but it is important to review the assessment regularly in case anything within the system changes.