Legionnaires’ Disease


Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria, which are found in water and soil. People get Legionnaires’ disease by inhaling the bacteria through water droplets. The pneumonia caused by Legionella bacteria can be severe; however the majority of cases can be cured with antibiotics. Legionella bacteria thrive in warm water and are commonly found in hot tubs, pools, spas, and large plumbing systems. Most people exposed to the bacteria will not get sick, but the risk is highest for older people, smokers, and those with weakened immune systems.

Symptoms and Diagnosis

Symptoms of Legionnaires’ disease usually appear within 2 to 14 days after exposure to the bacteria. They usually begin with headache, muscle pain, chills, and a high fever (104 °F or 40 °C). After a few days other symptoms develop, including cough, shortness of breath, fatigue, gastrointestinal symptoms, and confusion. Severe cases can lead to lung failure, kidney failure, or septic shock (blood infection). Legionnaires’ disease is not contagious. Pontiac fever is a milder form of the disease that usually lasts only 2 to 5 days and does not cause pneumonia. The symptoms of Pontiac fever go away without treatment.

Legionnaires’ disease is diagnosed by confirming pneumonia and the presence of Legionella bacteria in the body. A physical exam or chest X-ray can detect pneumonia. A urine antigen test, culture from sputum or lung tissue, or blood test can confirm the presence of the bacteria. In cases with neurological symptoms such as confusion, a CT scan or spinal tap may be used.


Legionnaires’ disease is caused by infection with Legionella bacteria, which thrive in warm water environments such as hot tubs, cooling towers, hot water tanks, large plumbing systems, and decorative fountains. Most people get infected by breathing in mist or vapor that contains the bacteria, such as mist from a hot tub that has not been cleaned properly. Rarely, people can get Legionnaires’ disease by getting water in the lungs (aspiration) or from soil. Once the bacteria get into the body, they continue to grow in the lungs.

Most healthy people exposed to Legionella bacteria will not get sick. People with weakened immune systems are at the highest risk of getting Legionnaires’ disease. This includes older people, smokers, people with chronic lung conditions, or people with other illnesses that affect the immune system. There is also an increased risk of illness following surgery or during chemotherapy. Outbreaks of Legionnaires’ disease commonly occur in hospitals and nursing homes. Continue reading for Prevention and Treatment Information . . .

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