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Fast Facts

Español: Datos breves

  • Legionella can cause Legionnaires’ disease or Pontiac fever, collectively known as legionellosis.
  • The bacterium was named after an outbreak in 1976, when many people who went to a Philadelphia convention of the American Legion got sick with pneumonia (lung infection).
  • About 5,000 cases of Legionnaires’ disease are now reported each year in the United States. [1]
  • About one out of every 10 people who get sick from Legionnaires’ disease will die. [2]
  • People can get Legionnaires' disease or Pontiac fever when they breathe in a mist (small droplets of water in the air) that has been contaminated with Legionella.
  • In general, Legionnaires’ disease is not spread from one person to another. However, this may be possible in rare cases. [2]
  • Legionella is found naturally in fresh water environments, like lakes and streams, but can become a health concern in human-made water systems.
  • Keeping Legionella out of water systems in buildings is key to preventing infection.


  1. Dooling KL, Toews KA, Hicks LA, et al. Active Bacterial Core Surveillance for Legionellosis–United States, 2011–2013. MMWR Morb Mortal Wkly Rep. 2015;64(42):1190–3.
  2. Correia AM, GonCalves J, Gomes, JP, et al. Probable Person-to-Person Transmission of Legionnaires' Disease. N Engl J Med. 2016;374:497–8.