Nosocomial Legionnaires' disease: a continuing common-source epidemic at Wadsworth Medical Center.

Forty-nine cases of Legionnaires' disease were identified from May 1977 through July 1978 in patients and employees at Wadsworth Medical Center. Cases clustered in October and November 1977. Fifteen patients died. All Legionnaires' disease (LD) patients were in the hospital before onset of illness (median time from admission to onset, 17 days; range, 3 to 276 days). Twenty patients were immunosuppressed or compromised by malignancy. In 1977, six of 12 renal-homograft recipients acquired LD pneumonia in contrast to three of 22 during the preceding 3 years (P = 0.031, Fisher's exact test). In a prospective survey of 1658 consecutive hospital admissions, seven cases of Legionnaires' diseases occurred (0.4%), including six among 14 patients who seroconverted to the LD bacterium. Prevalence of a reciprocal titer of 128 or above in Wadsworth employees was significantly greater than in a nearby control population (P = 0.044, Fisher's exact test). Exposure to the external hospital environment may be an important factor, and soil may be a reservoir for the LD bacterium. Legionnaires' disease at Wadsworth may be a nosocomial pneumonia affecting a small group of patients with particular risk factors.