Legionnaires' disease

Article By:

Hoffman, Paul S. School of Medicine, University of Virginia, Charlottesville, Virginia.

Last reviewed:August 2020

DOI:https://doi.org/10.1036/1097-8542.376000

A type of pneumonia usually caused by infection with the bacterium Legionella pneumophila, but occasionally with a related species (such as L. micdadei or L. dumoffii). More than 40 species of Legionella are known, though not all have been associated with disease. The disease was first observed in an epidemic among those attending an American Legion convention in Philadelphia, Pennsylvania, in 1976. The initial symptoms are headache, fever, muscle aches, and a generalized feeling of discomfort. The fever rises rapidly, reaching 102–105°F (32–41°C), and is usually accompanied by cough, shortness of breath, and chest pains. Abdominal pain and diarrhea are often present. Diagnosis is often difficult, though there are several rapid diagnostic kits, including a urine antigen test that can augment chest x-ray presentation of a patchy interstitial infiltrate (atypical pneumonia in the case of Legionnaires' disease). Proper diagnosis is important since the mortality rate can be as high as 15% in untreated or improperly diagnosed cases. Erythromycin, new-generation fluroquinolones, and rifampicin are considered highly effective medications, whereas the penicillins and cephalosporins are ineffective.

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