Legionnaire disease (LD) is a type of pneumonia caused by Legionella pneumophila, a flagellated gram-negative bacterium found primarily in warm water environments. The disease and the bacterium were discovered following an outbreak traced to a 1976 American Legion convention in Philadelphia. A number of risk factors for acquiring LD have been identified, including age, smoking, chronic lung disease, cancer, and immunosuppression (summary by Hawn et al., 2003). [from
OMIM]