Continuous Disinfection by Monochloramine on Domestic Hot Water System of Health-care Facilities for the Control of Legionella Contamination in Italy

Backgroud: The prevention of Legionella spp. colonization of water distribution systems is a critical issue in healthcaresettings and only an effective disinfection of water systems and appropriate environmental surveillance strategies allow to preventnosocomial legionellosis. Methods: Due to the temporary effectiveness (increase of the temperature of water in boilers and shockhyperchlorination), the high costs (point-of-use water filters) or the ineffectiveness (hydrogen peroxide, H2O2) of the previous controlprocedures, 3 devices (one for each hot water loop) continuously injecting monochloramine have been installed in two different Italianhospitals heavily contaminated by Legionella pneumophila SG3 and SG6. Aim: To evaluate the efficacy of continuous disinfection bymonochloramine for control of Legionella on domestic hot water (DHW) distribution system of health-care facilities. Findings: Onemonth after the disinfection of DHW with monochloramine, the load of L. pneumophila SG3 and SG6 (previous mean count rangingfrom 10^3 to 10^5 CFU/L), as well as the Heterotrophic Plate Count (HPC) (previous mean count ranging from > 10^2 to > 10^4 CFU/mL),decreased at undetectable levels in 100% of the sampling points in the two hospitals. Conclusion: The results suggest that continuousinjection of monochloramine on DHW systems can fully control L. pneumophila and HPC in contaminated hospitals since thebeginning of its application.