Intermittent Use of Copper-Silver Ionization for Legionella Control in Water Distribution Systems: A Potential Option in Buildings Housing Individuals at Low Risk of Infection

ZEMING LIU, JANET E. STOUT, MARCIE BOLDIN, JOHN RUGH, WARREN F. DIVEN, VICTOR L. YU
OXFORD ACADEMIC, CLINICAL INFECTIOUS DISEASES, JANUARY 1998

Introduction
This study evaluated three healthcare facilities colonized with Legionella to determine if:

1. The disinfection effects of copper-silver ionization remain after inactivating the system.
2. A facility could use one copper-silver ionization unit and rotate it between two buildings.
3. Copper and silver ions were present in the biofilm, providing residual protection.

Results
The Legionella positivity rate (percentage of test sites positive for Legionella) was significantly reduced for the two test buildings using copper-silver ionization.

• First test building: Legionella positivity reduced from 50% to 0% after four weeks
• Second test building: Legionella positivity reduced from 80% to 0% after 12 weeks
• Control building (no copper-silver ionization): Mean positivity rate of 83% for study duration

Both test buildings remained Legionella-free for six to eight weeks after deactivating the copper-silver ionization system. The researchers found high concentrations of copper in the biofilm and suggested this to be the reason that early recolonization of Legionella was prevented.

Conclusion
Because copper-silver ionization provides a residual effect of preventing early recolonization of Legionella, it is possible to rotate one copper-silver unit between several buildings. The study explained that this method could be considered for facilities that house individuals at low risk for contracting Legionnaires’ disease.