Legionnaire's disease

Last reviewed 01/2018

Legionnaire's disease is a severe form of pneumonia caused by the gram negative bacterium Legionella pneumophila. The bacterium is named because it was the cause of an outbreak of pneumonia at an American Legion Convention in 1976.

Legionnaire's disease should be suspected if the patient presents with three of the following:

  • prodromal virus-like illness
  • initial dry cough, confusion, diarrhoea
  • hyponatraemia
  • leukocytosis