Prolonged effect of two combined methods for Legionella disinfection in a hospital water system.

This study was conducted in our 650 bed general hospital, which is situated on the southern outskirts of Milan (Italy). After a first nosocomial case of pneumonia (caused by Legionella pneumophila serogroup 1), we first used a conventional method (heat shock) without success. To solve the problem we then tried a copper-silver ionization system combined with a chlorine dioxide device. During the four years after the installation of these two systems we recorded a significant (p < or = 0.05) reduction in Legionella colonization, and no new cases of Legionnaires' disease were observed. Our results suggest that the Cu-Ag ionization system, combined with a chlorine dioxide device, is a highly promising method for the control of Legionella pneumophila in a hospital water distribution system.