Strategies for infection control of nosocomial Legionnaires' disease: four-year surveillance experience in a teaching hospital in Italy.

The degree of Legionella pneumophila contamination in hospital water supplies has been shown to correlate with the incidence of nosocomial Legionnaires’ disease (LD). Within the context of the Italian Multicentric Study of Legionellosis, the authors carried out a 4-year active prospective LD surveillance program in a large university hospital in Rome. They assessed the usefulness of the hospital water monitoring program to predict the risk of nosocomial LD. A monthly decontamination procedure of the intermediate tanks is carried out, which consists of mechanically cleaning out the tanks to remove the formed organics, followed by washing out the tanks with sodium hypochlorite. Once the nosocomial LD case had occurred, epidemiological and environmental investigations were performed in the hospital ward involved. The low incidence of nosocomial LD cases in the hospital during the study period seems to be correlated to the low contamination level of L. pneumophila (20% of positive samples in 4 years) in hospital wards and to a low percentage of positive water samples per semester of surveillance. An infection control system for nosocomial LD should therefore be based on both environmental and clinical surveillance, together with the appropriate maintenance of the hospital water distribution system.