The incidence of legionella pneumonia: a 1-year prospective study in a large community hospital.

In a 1-year prospective study, 28 of 476 pneumonia patients (5.9%) were diagnosed as having legionella pneumonia. Legionella pneumonia was diagnosed in 12 (5%) of 240 community-acquired pneumonias and in 16 (6.8%) of 236 nosocomial pneumonias. Four methods of establishing diagnosis were used: serum antibody detection, direct proof of legionellae by immunofluorescence, culture, and legionella antigen detection in urine. The latter method proved to be clearly advantageous to all other methods in establishing the diagnosis. Twelve of the 28 patients (42.8%) died; all of them had severe underlying diseases. The fatality rate in patients treated with erythromycin was 18.8% (3/16 cases) and 75% (9/12 cases) in patients treated with antibiotics other than erythromycin. In 57.1% (16/28 patients) legionella pneumonia was acquired nosocomially. The results of our study underscore the need to use a broad spectrum of legionella diagnostic methods routinely and to administer antibiotics effective against legionellae in cases of pneumonia of unknown cause.