Nosocomial Legionnaires' disease: Clinical and radiographic patterns.

From 1981 to 1991, 55 patients (33 males, 22 females, mean age 58.6 years) with nosocomial Legionnaires' disease were studied. The mortality rate was 64%. One-half of the patients developed nosocomial Legionnaires' disease within three weeks of admission. A surprising clinical feature was the low rate of findings of consolidation on physical examination, despite the fact that 52% of patients had this finding on chest radiograph. More than one-half of patients had pre-existing lung disease, rendering a radiographic diagnosis of pneumonia due to Legionella pneumophila impossible in 16% of cases despite microbiological confirmation. Nineteen per cent of patients who had blood cultures done had a pathogen other than L pneumophila isolated, suggesting dual infection in at least some of the patients. When the clinical and radiographic findings were combined it was noted that 40% of patients had one of three patterns suggestive of nosocomial Legionnaires' disease: rapidly progressive pneumonia, lobar opacity and multiple peripheral opacities. However, in 60% of patients there were no distinctive features.