Legionnaires' Disease and Pontiac Fever (Legionellosis)

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Legionnaires' disease and Pontiac fever (legionellosis) facts

  • Legionellosis is an infection that is caused by a bacterium.
  • The bacterium thrives in the mist that is sprayed from air-conditioning ducts.
  • The bacterium can infest an entire building.
  • The illness takes two distinct forms: Legionnaires' disease and Pontiac fever.
  • Legionnaires' disease is the more severe form and can be fatal.
  • Pontiac fever is the far milder form of the illness.
  • Symptoms of Legionnaires' disease include fever, chills, and a cough.
  • At its worst, Legionnaires' disease can cause severe pneumonia and respiratory failure.
  • Although antibiotics are effective for treatment, the most useful approach is prevention.

What causes legionellosis? What is the history of Legionnaires' disease?

Legionellosis is an infection that is caused by the bacterium Legionella pneumophila. The disease has two distinct forms:

  • Legionnaires' disease is the more severe form of the infection, which may involve pneumonia. The onset of this form of the disease is usually two to 10 days after infection but can occur up to 16 days later. Legionnaires' disease acquired its name in 1976 after an outbreak of pneumonia occurred among people attending a convention of the American Legion in Philadelphia. Later, the bacterium causing the illness was named Legionella pneumophila.
  • Pontiac fever is a milder illness that develops from hours to two days after initial infection and resolves spontaneously.
X-ray image of lungs of patient with Legionnaires' disease
X-ray image of lungs of patient with Legionnaires' disease; SOURCE: CDC
Medically Reviewed by a Doctor on 10/20/2014

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Prognosis of Legionnaires' Disease

How serious is it? What is the treatment?

Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases. Most cases can be treated successfully with antibiotics (drugs that kill bacteria in the body), and healthy people usually recover from infection.

Where do Legionella bacteria come from?

The Legionella bacteria are found naturally in the environment, usually in water. The bacteria grow best in warm water, like the kind found in hot tubs, cooling towers, hot water tanks, large plumbing systems, or parts of the air-conditioning systems of large buildings. They do not seem to grow in car or window air-conditioners.