The genus Legionella includes 26 species of which L. pneumophilia is most frequently associated with human disease. Legionella spp. are known to infect humans by inhalation. The ingestion of drinking water containing Legionella is considered irrelevant until the bacteria are amplified by multiplying in specific sites under thermal enrichment. Therefore, hot-water systems maintained below 60oC, such as cooling towers, spas, warm water systems in buildings may promote the growth of Legionella. Some of Legionella species are soil born and are commonly found in natural sources of freshwater.
Legionella infections are responsible for two types of disease: legionellosis and Pontiac fever. Legionellosis is commonly characterized by typical symptoms of pneumonia, such as high fever. Approximately 10% of legionellosis cases are fatal. Pontiac fever is a milder disease with a higher infection rate. The symptoms resemble the ones of influenza, including headache, vomiting and aching muscles. No fatal cases have been reported.
