Legionella pneumophila contamination of a hospital humidifier. Demonstration of aerosol transmission and subsequent subclinical infection in exposed guinea pigs.

Water from a humidifier located in the hospital was found to be contaminated with Legionella pneumophila, serogroup 1. The source of water for the humidifier was the hospital potable water system. Exposure of culture mediums to the humidifier aerosols yielded L. pneumophila, serogroup 1. Exposure of guinea pigs to humidifier aerosols produced a subclinical infection as demonstrated by seroconversion to L. pneumophila. Seroconversion rate of guinea pigs to L. pneumophila was higher when greater quantities of L. pneumophila were present in the water; a corresponding increase in recovery of the organism from culture mediums exposed to aerosols was also seen. This report shows that mechanically created aerosols of Legionella-contaminated potable water might be the vehicle of transmission of Legionnaires' disease, especially in the hospital setting.