Use of copper-silver ionization for the control of legionellae in alkaline environments at health care facilities

Am J Infect Control. 2015 Sep 1;43(9):971-6. doi: 10.1016/j.ajic.2015.05.018. Epub 2015 Jul 3.


Background: There are multiple treatment options for the control of legionellae in premise hot water systems. Water chemistry plays a role in the efficacy of these treatments and should be considered when selecting a treatment. This study demonstrated the efficacy of copper-silver ionization (CSI) under alkaline water conditions in 2 health care facilities.

Methods: Monitoring for copper (Cu) and silver (Ag) ions was performed, and the corresponding percentage of positive Legionella cultures was monitored. Low Legionella colony forming units (CFU), with a mean <10 CFU/100 mL, and ≤30% positive culture for each sampling period, along with no recurrent disease, were considered indicative of control.

Results: CSI treatment was shown to reduce both the number of CFU found and the percentage of samples found to be culture positive. After treatment was established, culture positivity was, for example, reduced from 70% (>10(3) CFU/100 mL) to consistently <30% (38 CFU/100 mL).

Conclusion: Control of legionellae in premise water systems may be a complex process requiring long-term assessments for adequate control. This work found that CSI could be successful in controlling Legionella under alkaline water conditions, and the evidence suggests that Ag ions are responsible for the control of Legionella pneumophila 1, L pneumophila 6, and L anisa.

Keywords: Alkaline environment; Chlorine dioxide; Copper-silver ionization (CSI); Hospital; Legionella; Legionellosis; Nursing home; Percentage positivity.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Colony Count, Microbial
  • Copper / pharmacology*
  • Cross Infection / prevention & control*
  • Disinfection / methods
  • Health Facilities
  • Humans
  • Infection Control / methods
  • Legionella / drug effects*
  • Legionella pneumophila / drug effects
  • Legionellosis / microbiology
  • Legionellosis / prevention & control*
  • Legionnaires' Disease / microbiology
  • Legionnaires' Disease / prevention & control
  • Silver / pharmacology*
  • Water Microbiology*
  • Water Supply / standards


  • Silver
  • Copper