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Legionnaires' Disease

What is legionellosis?

Legionellosis (pronounced Lee-juh-nel-o-sis) is a lung infection caused by bacteria (germs) called Legionella pneumophila.

The disease has two distinct forms:
  • Legionnaires' disease: which is the more severe form with pneumonia
  • Pontiac Fever: a milder illness without pneumonia

Approximately 8,000-18,000 people get Legionnaires' disease in the United States every year. Many more cases may not be diagnosed or reported.

How do you get legionellosis?

Legionella germs are commonly found in many types of water/plumbing systems. They grow to high numbers in warm, stagnant water (90 - 105°F). Legionellosis may occur after a person breathes in mists or vapors (small droplets of water in the air) from a water source (e.g., air conditioning cooling towers, whirlpool spas, showers, humidifiers) polluted with the germ. A person may be exposed to these mists or vapors in homes, hotels, workplaces, hospitals, cruise ships or other public places. The germ is NOT passed from person to person, and there is no proof of people becoming infected from car air conditioners or household window air conditioning units.

People who are most at risk of getting sick from legionellosis include the elderly, smokers, patients with chronic lung disease (like emphysema) and those with weak immune systems from diseases (like cancer, diabetes and kidney failure). Legionnaires' disease is a sporadic and local problem in hospitals and nursing homes, where germs may spread easily and people are more likely to become infected.

How do you know if you have legionellosis?

People with Legionnaires' disease can have some or all of the following symptoms:
  • Fever
  • Tiredness
  • Diarrhea
  • Cough (dry or may produce mucus)
  • Chills
  • Loss of appetite
  • Muscle aches
  • Headache
Symptoms of Legionnaires' disease usually appear within two to 10 days after having contact with the germ. A person with Pontiac fever will have fever and muscle aches but not pneumonia. Symptoms of Pontiac fever usually appear within a few hours to three days, and usually clear after five days.

What are the serious health problems you can get from legionellosis?

The serious health problems you can get from legionellosis include respiratory failure, septic shock and acute kidney failure. Legionnaires' disease can be very serious and can cause death in up to 5% to 30% of cases.

How is legionellosis treated?

Most cases of Legionnaires' disease can be treated successfully with antibiotics (drugs that kill bacteria in the body), and healthy people usually recover from infection. Pontiac fever usually goes away on its own without treatment. If you think you have legionellosis, talk with your health care provider.

How is legionellosis tested?

The most useful tests find signs of legionella in urine, blood tests, sputum or lung tissue. Sometimes, a chest X-ray or CT scan of the lungs may be needed for further analysis.

How can legionellosis be prevented?

Legionellosis can be prevented by improved design and upkeep of cooling towers and plumbing systems, and thorough cleaning and disinfecting of such water systems. Additionally, avoiding smoking can greatly reduce the risk of legionellosis infection.

Download a full copy of the fact sheet.

For additional resources, please call Contra Costa Public Health Communicable Disease Programs at 925-313-6740.

Centers for Disease Control and Prevention
L.A. County Department of Public Health
The Mayo Clinic


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