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Air conditioning units are a potential source of Legionnaires' disease.

Air conditioning units are a potential source of Legionnaires' disease.
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Legionnaires' disease

Legionnaires' disease is a severe and sometimes life-threatening form of pneumonia, or lung inflammation. It is caused by Legionella pneumophila bacteria. It is most commonly contracted by older people, smokers and people with weakened immune systems.

It is important that you contact your doctor as soon as possible if you think that you have been exposed to Legionella bacteria.

Legionnaires' disease symptoms

People with Legionnaires' disease usually get sick between two and 10 days after being infected. The symptoms are similar to those of the flu, including:

Within two or three days other symptoms may also develop, such as:

Legionnaires' disease diagnosis

Legionnaires' disease is diagnosed in the same way as other forms of pneumonia. Your doctor may listen to your chest with a stethoscope or ask for a chest X-ray. You may be asked to give samples of mucus, blood or urine.

Legionnaires' disease treatment

Legionnaires' disease is generally treated using antibiotics. Some people will need to be treated in hospital.

Legionnaires' disease prevention

Legionnaires' disease is not transmitted from person to person. It is usually picked up from water systems like air conditioning units, cooling towers, pools, baths and showers. Careful cleaning of these water systems can help prevent Legionnaires' disease.

Smoking increases the risk of infection for people exposed to airborne Legionella bacteria.


Mayo Clinic (Legionnaires’ disease - Definition), Mayo Clinic (Legionnaires’ disease - Symptoms), MyVMC (Legionnaire’s disease (Legionella pneumonia; Pontiac fever)), Mayo Clinic (Legionnaires’ disease - Tests and diagnosis), Mayo Clinic (Legionnaires’ disease - Prevention)

Last reviewed: July 2015

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