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

• Remediating premise water systems is complex and may require long-term assessment.
• Chlorine dioxide had limited success controlling Legionella in a complex hospital environment.
• Copper-silver ionization was effective at pH values of 8.7-9.9 against both Legionella pneumophila and L anisa.
• Silver ions may have played the main role in controlling the legionellae.
• There has been no recurrence of disease in locations with chlorine dioxide or copper-silver treatment.

BackgroundThere 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.MethodsMonitoring 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.ResultsCSI 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% (>103 CFU/100 mL) to consistently <30% (38 CFU/100 mL).ConclusionControl 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.

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