Legionnaires’ disease


Legionnaires’ disease is an airborne disease caught by inhaling small droplets of contaminated water. It is not contagious and is not known to spread directly from person to person. It cannot be caught by drinking contaminated water.


Legionella bacteria are common in natural water sources such as rivers, lakes and reservoirs, usually in low numbers. The risk of the disease is present when water is stored or recirculated in man-made water systems. Contamination can develop and spread in purpose-built systems like cooling towers, evaporative condensers, hot and cold water systems and whirlpool spas, humidifiers, air-washers, emergency showers and indoor water fountains. Problems develop when bacteria spread quickly through water-based systems in warm temperatures (between 20 degrees C to 45 degrees C).


In 2012, two legionnaires’ outbreaks in Edinburgh and Stoke-on-Trent caused seven deaths and left more than 120 members of the public ill. The Crown Office and Procurator Fiscal Service (COPFS) announced that no one would be prosecuted over the Edinburgh outbreak, as an investigation was unable to identify the source of the bacteria. Lawyers representing people affected by the outbreak called for a fatal accident inquiry (FAI) to be held into the case. Inquests into the deaths in the Stoke on Trent outbreak have recently taken place.


Following the outbreaks, the HSE released a new, significantly revised and more detailed (version 4) of the Approved Code of Practice (ACOP) Legionnaires’ Disease: The control of Legionella bacteria in water systems (L8).

The ACOP, along with supporting Technical Guidance, provides practical advice to employers on how to control the risk of legionella bacteria in water systems. The guidance is available from the Legionnaires’ Disease pages of the HSE website along with Legionnaires’ disease, A brief guide for duty holders and Management of the risks from legionella in cooling towers and evaporative condensers
, known as HSG274.