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Legionnaire Disease and Pontiac Fever (cont.)

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How is Legionnaires' disease spread?

Outbreaks of legionellosis have occurred after people have inhaled aerosols that come from a water source (for example, air-conditioning cooling towers, whirlpool spas, or showers) contaminated with Legionella bacteria. People may be exposed to these aerosols in homes, workplaces, hospitals, or public places. Infection cannot be acquired from another person with legionellosis, and there is no evidence of people becoming infected from vehicle air conditioners or household window air-conditioning units.

Cases of Legionnaires' disease have increased throughout the United States, but this most likely represents increased detection by better diagnostic tests. Some would suggest that this increase may be due to global warming, though this seems unlikely.

Hospital-acquired infections have occurred and are usually due to contamination of the water supply. Two well-reported cases occurred in the 1980s in Los Angeles, one at the Wadsworth VA hospital and the other at the City of Hope. Guidelines have now been established for routine environmental testing for Legionnaires' in several states in the United States and by the Veterans Affairs health care system.

With regard to travel-associated infection, this usually occurs in hotels from contaminated water, most notably at the Legionnaires' convention in Philadelphia. This disease has also been associated with travel on cruise ships.

Some data suggest an increase incidence of Legionnaires' in the elderly in nursing homes linked to eating puréed food, probably also due to increased aspiration in this population.

How common is Legionnaires' disease?

Legionnaires' pneumonia is not uncommon. In fact, it represents over 4% of all community-acquired pneumonias. An additional unknown number of people are infected with the Legionella bacterium but have only mild symptoms or no symptoms at all (so-called Pontiac fever).

Outbreaks of Legionnaires' disease have received the most media attention. An outbreak was associated with a party at the Playboy mansion in Los Angeles where at least four individuals contracted Legionnaires' disease. However, the disease most often occurs as single, isolated cases not associated with any identified outbreak. Outbreaks are usually recognized in the summer and early fall, but cases may occur all year long. More recently, outbreaks have been detected in gym participants in Florida and in a police station in New York.

Since the bacterium of Legionnaires' disease was identified in 1976, numerous hospital-acquired outbreaks of the disease have also been reported. These outbreaks have enabled researchers to study epidemics of legionellosis. A recent CDC evaluation reported that one in five Legionnaires' disease cases are linked to health care facilities.

Medically Reviewed by a Doctor on 6/22/2017


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