Four years of experience with silver-copper ionization for control of legionella in a german university hospital hot water plumbing system

Clin Infect Dis. 1999 Dec;29(6):1507-11. doi: 10.1086/313512.


Silver-copper ionization was used for controlling Legionella distribution in a German university hospital hot water plumbing system for 4 years. In the beginning, silver concentrations were not allowed to exceed 10 microg/L because of drinking water regulation limits in Germany. Water samples were monitored for Legionella counts, temperature, and silver and copper concentrations. A significant (P<.001) 3.8-log reduction of Legionella counts, from 40, 000 cfu/L to 7 cfu/L, was found during the first year with silver-copper ionization. Nevertheless, the long-term efficacy of silver concentrations <10 ,++microg/L was not sufficient. Legionella counts increased to 10,000 cfu/L during the third year. During the fourth year, we studied the influence of higher silver concentrations on Legionella distribution. With an average silver level of 30 microg/L, only a 1.3-log reduction in Legionella, to 500 cfu/L, was achieved. The effect was not significant (P=.071); therefore, it must be considered that Legionella developed a tolerance to silver ions.

Publication types

  • Comparative Study

MeSH terms

  • Chlorine / pharmacology
  • Colony Count, Microbial
  • Copper / pharmacology*
  • Cross Infection / microbiology
  • Cross Infection / prevention & control*
  • Dose-Response Relationship, Drug
  • Germany
  • Hospitals, University
  • Humans
  • Infection Control / methods
  • Legionella pneumophila / drug effects*
  • Legionnaires' Disease / prevention & control*
  • Multivariate Analysis
  • Silver / pharmacology*
  • Temperature
  • Time Factors
  • Water Microbiology
  • Water Supply*


  • Silver
  • Chlorine
  • Copper