Legionnaires' disease and other newly recognized Legionella-like causes of bacterial pneumonia.

Three "new" pneumonias have recently been recognized which are old diseases whose etiology has only been newly-recognized. Legionella pneumophila (Legionnaires' disease), Pittsburgh Pneumonia Agent (PPA), and Legionella-like Organisms (the Family Legionellaceae) are "rickettsia-like" bacteria which require special media for cultivation. They can each cause nosocomial pneumonia in immunosuppressed patients and all but PPA cause community-acquired pneumonia. The Legionellaceae reside in the environment within water and soil. Diagnosis can be established by morphologic, microbiological, and immunologic analysis of respiratory secretions or lung tissue. It may be confirmed retrospectively by serology. Legionella pneumophila and PPA are susceptible to erythromycin and rifampin; erythromycin is the current drug of choice for treatment of these diseases.