[Legionnaires' disease].

Among community-acquired pneumonias or hospital-acquired pneumonias, the genus Legionella, an intracellular bacteria, is one of the most important pathogens causing death. The bacteria from clinical specimens could not be cultured by ordinary methods and the polymerase chain reaction, a new method for rapid detection, has been developed; however, Legionella pneumonias are still difficult to diagnose. Antibiotics, such as macrolides, new quinolones and rifampicin, are very active against Legionella spp. These antibacterial agents should be administered when acute pneumonia tends to exacerbate with previous beta-lactams or aminoglycosides therapy. Legionella pneumonias are more likely to occur in elderly males or in the compromised-hosts with underlying diseases, such as malignancy, diabetes mellitus, AIDS, etc.