Legionnaires’ Disease in Hot Water

Sources: Miuetzner S, et al. Efficacy of thermal treatment and copper-silver ionization for controlling Legionella pneumophila in high-volume hot water plumbing systems in hospitals. Am J Infect Control 1997;25:452-457; Liu Z, et al. Intermittant use of copper-silver ionization for Legionella control in water distribution systems: A potential option in buildings housing individuals at low risk of infection. Clin Infect Dis 1998;26:138-140.

Two cases of legionnaires’ disease occurred at a university childrens’ hospital; the clinical isolates of L. pneumophila matched those recovered from the hospital’s hot water system. The hot water supply consisted of three separate systems, each with its own large-volume storage tank.

Miuetzner and colleagues attempted to control Legionella colonization of the water system by the intermittent heat and flush method. Although Legionella was temporarily eliminated from the water, organism levels returned to pre-treatment levels within 30-60 days after the procedure. They installed silver copper ion generators in each of the three separate hot water systems in the hospital. Within one month of installation, rate of Legionella recovery fell from 60-80% of distal sites to less than 4% of distal sites. The efficacy of treatment was maintained over 22 months of follow-up. None of the hot water samples taken from faucets had copper levels that exceeded the EPA standard of 1300 PPB, and only 2% had levels exceeding the EPA standard for silver of 100 PPB. However, copper concentrations from samples taken from the bottom of storage tanks were as high as 128,000 PPB. No new cases of Legionnaires’ disease occurred during the follow-up period.

Liu and colleagues sequentially treated the hot water systems of two buildings in a long-term VA psychiatric facility with silver-copper ionization, rotating a single ion generator between the two. The hot water systems were low-volume systems using instantaneous steam heaters without storage tanks. A third building was not treated. In the first building, Legionella were undetectable within four weeks and remained so for the duration of treatment (12 weeks). Legionella were first detected 12 weeks after the cessation of treatment. In the second building, Legionella were eradicated within 12 weeks and were first detected 12 weeks after the end of treatment. The difference in time to clearance of Legionella between the two systems appeared to be related to a slower rate of rise of silver and copper concentrations in the latter. Concentrations of copper, but not of silver, were significantly higher in biofilm samples than in free-water samples. The third building was left untreated and showed no decline in Legionella colonization.


Many hospital hot water systems are colonized with Legionella; colonization of the water system presents a significant risk of acquisition of Legionella pneumonia to susceptible patients.1 Reduction of the levels of the organism leads to a reduction in the incidence of nosocomial Legionnaires’ disease. At present, there are a number of options for decontamination of the water system. Intermittent heating and flushing is the simplest; it involves raising the hot water temperature to 70°C, maintaining a temperature of at least 60°C peripherally, and flushing distal sites for 30 minutes. This procedure is typically associated with a rapid reduction in Legionella. It has several advantages. It can be instituted almost immediately in the event of an outbreak and requires no special equipment. However, it is rather labor intensive and could potentially expose patients and staff to scalds. Unfortunately, Legionella regrowth to pre-treatment levels invariably occurs after a variable period of time, and the procedure must be repeated indefinitely. Hyperchlorination can be effective in eradicating Legionella but has several notable disadvantages. Chlorine levels are difficult to maintain in hot water, and recolonization occurs rapidly after an interruption in chlorination. High levels of chlorine are highly corrosive to pipes. Chlorine is reactive with a variety of organic molecules; the resulting compounds are potentially carcinogenic.

Silver-copper ionization has several advantages. It is highly effective in eliminating Legionella. The cost is moderate (approximately > $30,000 per unit). Copper ions are concentrated in biofilms and in the sediment of hot water tanks, areas that are major reservoirs for Legionella replication. Because of this, there is considerable residual protection against re-colonization should the unit be out of service; it takes 8-12 weeks for Legionella to reach pre-treatment levels.

Although not difficult to implement, silver-copper ionization is not a "plug it in and forget it" system. Periodic monitoring of ion levels and of Legionella colonization is required; a modest amount of system maintenance is required. Areas of low water use may not be adequately treated because of lack of constant delivery of ions to those portions of the system. There are occasional episodes of discolored water, usually due to excess silver levels. This may occur when large changes in water pressure or usage patterns flush water from relatively stagnant areas of the system. Silver and copper ion concentrations could then temporarily exceed recommended levels. Fortunately, people rarely drink hot water, and the cold water system is unaffected.

With proper attention to maintenance, monitoring of ion levels, and periodic surveillance cultures for Legionella in the water system, silver-copper ionization is highly effective and without serious drawbacks. I believe that, as more evidence accumulates, it will prove to be the preferred method for the eradication of Legionella from hospital water systems.


1. Stout JE, Yu VL. N Engl J Med 1997;337:682-687.

Intermittent heating and flushing to reduce the levels of Legionella in hot water systems requires:

a. maintaining a temperature of at least 60°C peripherally.

b. flushing distal sites for 20 minutes.

c. raising the hot water temperature to 70°C.

d. both a and c.

e. all of the above.