Overview

Legionnaires' disease is a severe form of pneumonia — lung inflammation usually caused by infection. Legionnaires' disease is caused by a bacterium known as legionella.

You can't catch legionnaires' disease from person-to-person contact. Instead, most people get legionnaires' disease from inhaling the bacteria. Older adults, smokers and people with weakened immune systems are particularly susceptible to legionnaires' disease.

The legionella bacterium also causes Pontiac fever, a milder illness resembling the flu. Separately or together, the two illnesses are sometimes called legionellosis. Pontiac fever usually clears on its own, but untreated legionnaires' disease can be fatal. Although prompt treatment with antibiotics usually cures legionnaires' disease, some people continue to experience problems after treatment.

Sept. 24, 2016
References
  1. Yu VL, et al. Epidemiology and pathogenesis of Legionella infection. http://www.uptodate.com/home. Accessed March 23, 2016.
  2. Legionella (Legionnaires' disease and Pontiac fever). Centers for Disease Control and Prevention. http://www.cdc.gov/legionella/index.html. Accessed March 22, 2016.
  3. Longo DL, et al., eds. Legionella infections. In: Harrison's Principles of Internal Medicine. 19th ed. New York, N.Y.: McGraw-Hill Education; 2015. http://accessmedicine.com. Accessed March 23, 2016.
  4. Yu VL, et al. Clinical manifestations and diagnosis of legionella infection. http://www.uptodate.com/home. Accessed March 23, 2016.
  5. Papadakis MA, et al., eds. Bacterial and chlamydial infections. In: Current Medical Diagnosis & Treatment 2016. 55th ed. New York, N.Y.: The McGraw-Hill Companies; 2016. http://www.accessmedicine.com. Accessed March 23, 2016.
  6. Yu VL, et al. Treatment and prevention of legionella infection. http://www.uptodate.com/home. Accessed March 23, 2016.