Prospective 3-Year Surveillance for Nosocomial and EnvironmentalLegionella pneumophila: Implications for Infection Control

Abstract

Objectives.To perform a 3-year, prospective surveillance program for legionnaires disease (LD) in a large university hospital in Rome, and to assess the usefulness of the hospital water monitoring program in predicting the risk of nosocomial LD.Methods.Samples from patients with new cases of nosocomial pneumonia were sent for legionella laboratory investigations. Meanwhile, water samples for bacteriological analysis were collected every 6 months from high- and medium-risk hospital wards (10 in total).Legionella pneumophilaisolates collected were serotyped and analyzed by pulsed-field gel electrophoresis.Results.From June 2001 through May 2004, the pneumonia surveillance identified one case of nosocomial LD among 43 cases of nosocomial pneumonia (2.3%). Environmental investigations detectedL. pneumophilain 12 (18.7%) of the 64 water samples, of which 50% belonged to serogroup 1. TheL. pneumophilacount and the percentage of positive locations never exceeded 102colony-forming units/L and 20%, respectively, except when the LD nosocomial case occurred (positive water samples, 40%; I. pneumophila count, <102colony-forming units/L). Genotyping showed 3 prevalent clones ofL. pneumophilain the water distribution network, of which one persisted over the 3 years. One clone contained 3 differentL. pneumophilaserogroups (2, 4, and 6).Conclusions.The low incidence of nosocomial cases of LD appears to be associated with a low percentage (<20%) of positive water samples per semester and with a low contamination level (<102colony-forming units/L). 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.