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Legionellosis
(Legionnaires' Disease and Pontiac Fever)

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Medical Author:

George Schiffman, MD, FCCP

George Schiffman, MD, FCCP

Dr. Schiffman received his B.S. degree with High Honors in biology from Hobart College in 1976. He then moved to Chicago where he studied biochemistry at the University of Illinois, Chicago Circle. He attended Rush Medical College where he received his M.D. degree in 1982 and was elected to the Alpha Omega Alpha Medical Honor Society. He completed his Internal Medicine internship and residency at the University of California, Irvine.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Legionellosis (Legionnaires' disease and Pontiac fever) 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 is 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; SOURCE: CDC