Progress in the Control of Nosocomial Legionnaires’ Disease

Abstract & Commentary

Synopsis: Copper silver ionization in potable waters was found to be highly effective in reducing environmental Legionella colonization and preventing nosocomial Legionnaires’ disease over prolonged time periods.

Source: Stout JE, Yu VL. Experiences of the first 16 hospitals using copper-silver ionization for Legionella control: Implications for evaluation of other disinfection modalities. Infect Control Hosp Epidemiol. 2003;24:563-568.

The first 16 hospitals to install silver-copper ionization were surveyed in 1995 and again in 2000 to assess the efficacy of this method of environmental Legionella control. The water systems of all hospitals had been colonized with L pneumophila prior to installation of copper-silver ionization, and all had experienced cases of nosocomial Legionnaires’ disease. Twelve hospitals (75%) had tried other means of Legionella control prior to installation of copper-silver ionization and had found them to be unsatisfactory; these included heat-and-flush, hyperchlorination, and UV light, singly or in combination. The duration of operation of copper-silver ionization ranged from 5 to 11 years. After installation, the hospitals reported reduction in the frequency of isolation of Legionella from the water system; in 7 (43%), subsequent surveillance cultures were consistently negative, indicating complete eradication of the Legionella from the water system. In 15 of the 16 hospitals, no cases of nosocomial Legionnaires’ disease occurred after installation of copper-silver ionization. In the remaining hospital, a single case was identified shortly after installation; no cases were identified for the subsequent 7-year period.

The mean installation cost was $86,432 (range, $6000-134,000); annual maintenance costs ranged from $240 to $8000. Problems related to water quality were relatively few and consisted primarily of occasional water discoloration.

Comment by Robert Muder, MD

Legionnaires’ disease differs from other common causes of nosocomial bacterial pneumonia in that the reservoir of infection is the environment, eg, the hospital water system. Colonization of the hospital water system is highly predictive of the occurrence of nosocomial Legionnaires’ disease,1,2 and elimination of the organism from this reservoir is an effective means of prevention. The 1997 CDC recommendations for the prevention of nosocomial pneumonia recommended 2 methods for control of environmental Legionella colonization in hospitals that had experienced nosocomial Legionnaires’ disease. These were raising the hot water temperature to 65°C followed by flushing of distal outlets, or hyperchlorination to a chlorine level of 1-2 ppm. The CDC did not recommend copper silver ionization at that time, citing limited experience with that method.3

However, both of the recommended methods have some drawbacks. Heating and flushing is fairly labor intensive, and Legionella tends to recolonize the system in weeks to months after the procedure. High chlorine levels can be difficult to sustain in the hot water system, and high chlorine levels can accelerate corrosion of pipes. High levels of chlorine may also lead to the formation of potentially carcinogenic chlorinated organic compounds within plumbing systems.

The report by Stout and Yu indicates that copper-silver ionization is effective in controlling Legionella colonization and nosocomial Legionnaires’ disease over protracted periods of time. In addition, operation of the system was reasonable in terms of effort and cost. However, copper-silver ionization systems do require monitoring and maintenance for continued effectiveness. Periodic monitoring of copper and silver ion concentrations, and periodic culture surveillance for Legionella are highly desirable. The copper and silver electrodes need to be descaled periodically and may need to be replaced occasionally. This is well within the capability of most hospital engineering departments and infection control programs, as demonstrated by the fact that 16 diverse hospitals were able to use copper-silver ionization effectively for prolonged periods of time. It should now be considered a proven method of Legionella control in hospitals.

Dr. Muder is Hospital Epidemiologist Pittsburgh VA Medical Center Pittsburgh Section Editor, Hospital Epidemiology.


1. Yu VL, et al. Routine culturing for Legionella in the hospital environment may be a good idea: A three-hospital prospective study. Am J Med Sci. 1987;294:97-99.

2. Goetz AM, et al. Nosocomial Legionnaires’ disease discovered in community hospitals following culture of the water system: Seek and ye shall find. Am J Infect Control. 1998;26:6-11.

3. Centers for Disease Control and Prevention, Hospital Infection Control Practices Advisory Committee. Guidelines for the prevention of nosocomial pneumonia. MMWR Morb Mortal Wkly Rep. 1997;46(RR1): 1-79.