Legionnaires’ disease (legionellosis) is an infection caused by the bacterium Legionella pneumophila. It was first identified in 1976 after many attendees at an American Legion convention in Philadelphia suffered from pneumonia. The bacteria are found naturally in the environment, generally in warm water. Because the bacteria grow best in warm water, they have also been found in cooling towers, hot tubs, hot water tanks, large plumbing systems and decorative fountains.
People become sick when they breathe in contaminated water droplets through mist or vapors. Most people with legionellosis have pneumonia and some will require hospitalization. Others will have more severe complications and some will die from the infection. The Legionella bacteria can also cause Pontiac Fever, which is a milder form of legionellosis and does not cause pneumonia. Pontiac Fever will go away on its own after about 2-5 days and does not require treatment with antibiotics. People who are infected with Legionella bacteria can not spread it to other people; it is not contagious.
People most at risk from illness due to legionellosis are those aged 65 years or older, current and former smokers, those who are immunosuppressed or taking drugs to suppress the immune system, and people with chronic lung disease.
On average, between 8,000 and 18,000 people are hospitalized in the U.S. and 51 are diagnosed with Legionnaire’s disease in Connecticut annually. Many infections are not diagnosed or reported so these numbers may be higher. Summer and early fall are generally the times when more cases are seen; however, infection can happen during any season.
Outbreaks happen when two or more people become sick at the same time in the same place. This generally happens in buildings with complex water systems. Outbreaks have also been associated with whirlpool spas, cruise chips, and water used for drinking and bathing.
Legionnaires’ disease can be prevented by thorough cleaning of cooling towers according to guidelines and other warm water holding containers according to the manufacturer’s instructions.
Other helpful information
To contact the Epidemiology and Emerging Infections Program, please call 860-509-7994.