Legionellosis is caused by bacteria called Legionella. The disease has two different forms. Legionnaires’ disease is the more severe form of infection that causes pneumonia. Pontiac fever is caused by the same bacteria, but is a milder illness without pneumonia. The disease got its name after a group of people attending a convention of the American Legion in Philadelphia in 1976 developed pneumonia. Although the Legionella bacteria were around before 1976, scientists had never been able to find these bacteria in an ill person’s lungs before that time.

Reports of legionellosis cases and outbreaks are increasing in the United States and in Virginia. Legionellosis is caused by breathing in small water droplets containing Legionella bacteria. Outbreaks are commonly associated with buildings or structures that have complex water systems, such as hotels and resorts, long-term care facilities, hospitals, and cruise ships.

Antibiotics are used to treat Legionnaires’ disease. There is no vaccine to prevent legionellosis, but the presence of Legionella bacteria can be reduced by properly maintaining water systems where the bacteria grow (such as heating, cooling, and plumbing systems).