Legionella are a species of bacteria that cause a potentially fatal form of pneumonia, Legionnaires' disease, and a milder illness, Pontiac fever. Legionella bacteria are found in all aquatic environments and can become a risk to public health when they colonise artificial aquatic environments where they can become aerosolised and inhaled by humans. More than 61 species of Legionella exist, however, 90% of Legionnaires' disease cases are caused by Legionella pneumophila.

Common sources of Legionella include:

  • showers
  • cooling towers
  • air conditioning systems
  • humidfiers
  • spa pools

Cooling towers are most often implicated in larger clusters and outbreaks. Use of potting compost is associated with Legionnaires' disease caused by Legionella longbeachae.

Legionnaires' disease isn't common in Scotland and the majority of cases reported are related to travel outwith the country.