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 and 45 degrees Celsius).


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. The probable source of the Stoke-on-Trent outbreak was identified as a hot tub on display at the JTF Wholesale store in the town. The company was fined £1 million after pleading guilty to an offence under the Health and Safety at Work Act.


Following the outbreaks, the HSE released a new, significantly revised and more detailed version 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.