Controlling Legionella in hospital water systems: Experience with the superheat-and-flush method and copper-silver ionization

OBJECTIVE: To evaluate the effect of copper-silver ionization on Legionella colonization and nosocomial legionnaires' disease and to compare the effic acy of metal ions versus the superheat-and-flush method of disinfection. DESIGN: Prospective determination over a 36-month period of copper and silv er ion concentrations in the recirculating hot-water system, Legionella col onization of the hospital water distribution system, and cases of nosocomia l legionnaires' disease. Retrospective comparison of results with the previ ous 13 years, during which the superheat-and-flush method was used. SETTING: The Pittsburgh Veterans' Affairs Health Care System (University Dr ive Division) acute-care hospital. INTERVENTION: Three copper-silver ionization systems were installed on the hot water distribution system in November 1994. RESULTS: The average number of cases of legionnaires' disease per year and the percentage of distal sites positive for Legionella pneumophila for the superheat-and-flush method versus the copper-silver ionization method was s ix cases with 15% positivity versus two cases with 4% positivity, respectiv ely. The reduction in Legionella colonization after copper-silver ionizatio n was significant (P<.05) compared to the superheat and flush. Mean copper and silver ion concentrations (mg/L) were 0.29 and 0.054 hom hot-water tank s, and 0.17 and 0.04 from distal outlets, respectively. CONCLUSIONS: We conclude that a properly maintained and monitored copper-si lver ionization system was more effective than the superheat-and-flush meth od for reducing the recovery of Legionella from the hospital water distribu tion system.