Legionnaires' disease outbreak in an automobile engine manufacturing plant.

We investigated 4 cases of legionnaires' disease (LD) reported among workers at an Ohio automotive plant in March 2001. A "confirmed" case of LD was defined as x-ray-confirmed pneumonia and a confirmatory laboratory test. A "possible" case of LD was defined as elevated titers of antibody and respiratory symptoms. Legionella pneumophila serogroup 1 (LP1) was isolated from 1 case patient. Legionella was isolated from 18 (9%) of 197 environmental samples; 3 isolates were LP1 but did not match the case isolate. We conducted a case-control study; 17 case patients with confirmed or possible LD and 86 control subjects (workers with low antibody titers and without symptoms) were enrolled. Visiting a specific cleaning line (odds ratio, [OR], 7.29; 95% confidence interval [CI], 2.31-23.00) and working in the cleaning region of the plant (OR, 3.22; 95% CI, 1.11-9.38) were associated with LD. LD can be transmitted in industrial settings in which aerosols are produced. Clinicians should consider LD when treating persons from these settings for pneumonia.