La contaminazione da legionelle in ambiente ospedaliero. Risultati del monitoraggio delle reti di distribuzione dell’acqua calda in una Azienda ospedaliera

This study evaluated the presence and extent of contamination with Legionella spp. in the hot water distribution systems of three hospitals in Catania (Italy). In total, 291 hot water samples were collected between September 2002 and August 2005 and these were examined in order to monitor the hospital distribution systems and evaluate the efficacy of decontamination measures. L. pneumophila was detected at variable concentrations up to over 10000 UFC/L at several collection sites in some hospital buildings and branches of the water distribution system while other buildings/branches were found to be free of contamination. The most frequently isolated serogroup was L. pneumophila serogroup 3, occasionally associated with serogroups 4, 5 and 6. Molecular typing of Legionella strains by pulsed-field gel electrophoresis of genomic DNA restriction fragments identified four different genotypes, each recovered from a different branch of the distribution system. Decontamination procedures, including shock hyperchloration and two different thermal shock methods, performed between October 2003 and August 2005, led to only temporary reductions in contamination. In fact, previous concentrations of the same L. pneumophila serogroup were found within 3 to 8 months of decontamination. In order to prevent and monitor Legionella infections, sterilizing filters were installed in water taps of all wards with high-risk patients and urinary antigen testing was performed on all patients diagnosed with nosocomial pneumonia. No cases of Legionella pneumonia were identified in 2005.