Legionnaires' disease

Legionnaires' disease, also known as legionellosis or Legion fever, is a form of atypical pneumonia caused by any type of Legionella bacteria. Over 90% of cases of Legionnaires' disease are caused by Legionella pneumophila.

Other causative species include L. longbeachae, L. feeleii, L. micdadei, and L. anisa. These species cause a less severe infection known as Pontiac fever, which resembles acute influenza. These bacterial species can be water-borne or present in soil, whereas L. pneumophila has only been found in aquatic systems, where it is symbiotically present in aquatic-borne amoebae. It thrives in temperatures between 25 and 45 °C (77 and 113 °F), with an optimum temperature of 35 °C (95 °F). During infection, the bacterium invades macrophages and lung epithelial cells and reproduces within the infected cells.

Signs and symptoms

The length of time between exposure to the bacteria and the appearance of symptoms is generally two to 10 days, but can rarely extend to as much as 20 days. For the general population, among those exposed between 0.1 to 5% develop disease, while among those in hospital between 0.4 to 14% develop disease.