Legionella are ubiquitous aquatic saprophytes present world-wide. Many of these species are found in the environment and are also associated with human infections. L. pneumophila is an important species, which causes both community-acquired and nosocomial pneumonia.
Legionella as the causative agent of pneumonia was first identi-fied in 1976 during the annual convention of American Legion held at a hotel in Philadelphia. The infection was believed to be transmitted from the contaminated water in the hotel’s air con-ditioning system. A total of 182 cases were detected; of which 29 patients died because of the disease. The disease was charac-terized by fever, cough, and chest pain, leading to pneumonia and often death of the patient. This condition was referred to as Legionnaire’s disease, and the causative agent isolated from the fatal cases was designated as L. pneumophila.
Family Legionellaceae consists of one genus, Legionella which contains 39 genetically defined species and more than 60 serogroups. Many of these species cause infections in humans. Legionellosis is the term used for infections caused by different Legionella species. Legionnaire’s disease is the term used to describe the pneumonia caused by L. pneumophila.
L. pneumophila is the causative agent of Legionnaire’s disease, aswell as of Pontiac fever.