Legionellosis is a respiratory infection caused by bacteria in the Genus Legionella. Currently, there are approximately 50 species of Legionella consisting of 70 serogroups, but Legionella pneumophila serogroup 1 is responsible for about 95% of the Legionnaires' Disease cases in U.S.
The severity of legionellosis (the disease caused by Legionella) varies from a mild fever (called Pontiac fever) to a more serious pneumonia (called Legionnaires’ disease) that can affect anyone, but principally affects those who are more susceptible due to age, illness, immunosuppression or other risk factors, such as smoking.
Water is the natural reservoir for Legionellae, and the bacteria are found worldwide in many different natural and manmade aquatic environments, such as cooling towers; water systems in hotels, homes, ships and factories; respiratory therapy equipment; fountains; misting devices; and spa pools. The greatest concern is where water is aerosolized into small droplets; for example with showers, humidifiers, fountains, etc.
Since 2000, legionellosis has been on the rise and approximately 5,000 cases of Legionella are reported each year in the United States , however, the exact incidence of disease is difficult to determine since the symptoms can be similar the common cold.