Legionnaires' Disease

Legionnaires' disease, also called Legionellosis, is a serious infection caused by the Legionella pneumophila bacterium. This infection leads to inflammation of the lungs (pneumonia) and to other health problems.


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Legionella pneumophila


Pontiac fever

When Problems Are Legion

In 1976, a mysterious illness affecting the lungs suddenly struck more than 200 people attending an American Legion convention at the Bellevue Stratford Hotel in Philadelphia. The illness, dubbed Legionnaires' disease, killed 34 people in this outbreak. Eventually, the cause of the disease was identified as a previously unknown type of bacteria, named Legionella pneumophila, which were thriving in the warm still water of the hotel's air-conditioning system. It now is estimated that 10,000 to 15,000 cases of Legionnaires' disease occur in the United States each year.

The bacteria that cause Legionnaires' disease can live in many water sources, including hot water tanks, large air conditioners, and whirlpool spas. When these bacteria get into the air from the water, people can breathe them and become infected. For example, people might breathe bacteria that have been sprayed from a public air-conditioning system through cooling vents or from a hot water heater through a faucet. The disease cannot be passed from one person to another.

Anyone can catch Legionnaires' disease, although older adults and those who smoke cigarettes or have chronic * lung conditions seem to be at higher risk. People also are more likely to get the disease if their immune system (the body system that fights off infection) has been weakened by other conditions, such as cancer or AIDS, or by certain medications.

What Happens When People Get Legionnaires' Disease?


The symptoms of Legionnaires' disease start 2 to 10 days after a person is infected. They usually include high fever, chills, and coughing. The person also may have muscle aches, headache, tiredness, loss of appetite, and diarrhea. These symptoms get worse over a period of days. As part of the disease, the person develops pneumonia (noo-MO-nee-a), a serious inflammation * of the lungs. The person also may develop serious kidney problems.

* chronic (KRON-ik) means continuing for a long period of time.

* Inflammation is the body's reaction to infection, irritation, or injury that often involves swelling, pain, redness, and warmth.


As with most medical conditions, the doctor usually begins by giving the person a thorough exam and by asking about his or her medical history. A chest x-ray may show signs of pneumonia, and other lab tests may show signs of kidney failure. To check whether these problems are caused by Legionnaires' disease, the doctor must order special tests. These tests look for signs of the infection in the person's blood, urine, or sputum (mucus that is coughed up).


Legionnaires' disease is treated with an antibiotic, or bacteria-fighting drug, such as erythromycin (e-rith-ro-MY-sin). People with Legionnaires' disease often need to go to the hospital to receive extra fluids, to replace fluids lost due to high fever, and to receive oxygen to help treat the symptoms of pneumonia.

Pontiac Fever

Pontiac fever is a milder illness caused by the same bacteria that cause Legionnaires' disease. It usually strikes people who are otherwise healthy. The symptoms, including fever and muscle aches, start within hours after the person is infected.

Unlike Legionnaires' disease, Pontiac fever does not cause pneumonia. People with this disease usually recover in 2 to 5 days without treatment.

See also
Bacterial Infections


The U.S. Centers for Disease Control and Prevention (CDC), National Center for Infectious Diseases, Division of Bacterial and Mycotic Diseases, 1600 Clifton Road, Atlanta, GA 30333. CDC posts a fact sheet about Legionnaires' disease and Pontiac fever at its website.
Telephone 800-311-3435

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