Legionnaires' disease.

Legionella pneumophila infections frequently manifest themselves as a multisystem disease with acute pneumonia. Certain clinical and laboratory features are helpful in diagnosis but none are pathognomonic. Diagnosis frequently must be made clinically and erythromycin given presumptively because of the delay in seroconversion but culture and direct fluorescent antibody testing are quite useful for rapid diagnosis. Epidemiologic and laboratory investigations will undoubtedly yield considerable information about this fascinating bacterial disease.