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Fast Facts

Español: Datos breves

  • Legionella bacteria 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).
  • An estimated 8,000 to 18,000 people need care in a hospital due to Legionnaires' disease each year in the United States.1
  • Most people with Legionnaires' disease will have pneumonia since the Legionella bacteria grow and thrive in the lungs.
  • People get Legionnaires' disease or Pontiac fever when they breathe in a mist or vapor (small droplets of water in the air) that has been contaminated with Legionella.
  • Legionellosis is not spread from person to person.
  • Legionella are found naturally in the environment, usually in warm water.
  • Keeping Legionella out of buildings’ water supplies and cooling towers, as well as pools, hot tubs, and fountains, is key to preventing infection.


  1. Marston BJ, Plouffe JF, File TM Jr, Hackman BA, Salstrom SJ, Lipman HB, et al. Incidence of community-acquired pneumonia requiring hospitalization. Results of a population-based active surveillance Study in Ohio. The Community-Based Pneumonia Incidence Study Group. Arch Intern Med. 1997;157(15):1709–18.