Peer-Reviewed Research Study

Controlling Legionella in Hospital Drinking Water: An Evidence-Based Review of Disinfection Methods

YUSEN LIN, JANET E. STOUT, VICTOR YU
CAMBRIDGE UNIVERSITY PRESS, INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, FEBRUARY 2011

Introduction
This study reviewed the efficacy of different disinfection methods for controlling Legionella in hospitals, including copper-silver ionization, chlorine dioxide, hyperchlorination, monochloramine, UV, point-of-use filtration, and superheat-and-flush.

The four criteria each disinfection method must meet to validate efficacy include:

Proof it kills Legionella in a lab study.
Anecdotal reports of it controlling Legionella in individual hospitals.
Peer-reviewed reports of it controlling Legionella in individual hospitals over a prolonged period.
Confirmatory reports of it controlling Legionella in multiple hospitals over a prolonged period.

Results
A summary of findings for each disinfection method is included below.

Copper-silver ionization
– Only method validated by the four criteria
– Easy installation and maintenance
– Not impacted by higher temperatures
– Residual levels are maintained for a prolonged period
– Efficacy declines in pH greater than 8.5

Chlorine dioxide
– Penetrates biofilm
– Effective over a wide range of pH levels
– Creates harmful byproducts
– Difficult to maintain residual levels

Monochloramine
– Penetrates biofilm
– Effective over a wide range of pH levels
– Can cause anemia in dialysis patients
– On-site generation can be complicated

Hyperchlorination
– Most expensive and unreliable of all methods
– Causes corrosion
– Does not penetrate biofilm
– Introduces carcinogens into the water

Point-of-use filtration
– Effective against Legionella and Mycobacterium
– Provides immediate protection making them a good option for outbreaks
– Not cost-effective for long-term use

UV
– Non-chemical
– Works best when installed on the incoming water supply
– Does not provide systemic disinfection

Superheat-and-flush
– Effective in emergencies
– Not effective for prolonged use
– Limited to hot water lines

Conclusion
There are several viable methods for controlling Legionella, but copper-silver ionization was the only method validated by the four criteria at the time of this study. The researchers concluded that “copper-silver ionization appears to be the best available technology today for controlling Legionella colonization in hospital water systems.” They suggested that rigorous maintenance plans, regular monitoring of ion concentrations, and frequent Legionella testing are necessary to ensure long-term success.

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Highlighted author

Dr. Janet E. Stout

Dr. Janet E. Stout is the president and director of the Special Pathogens Laboratory, and a research associate professor at the University of Pittsburgh. A clinical and environmental microbiologist, Dr. Stout is internationally recognized for more than 30 years of research in Legionella and is credited as the first to demonstrate the link between Legionnaires' disease and the presence of Legionella in hospital water systems. Dr. Stout was instrumental in developing the first US prevention strategy for hospital-acquired Legionnaires' disease that now serves as the model for national Legionella guidelines. She serves on the Legionella standards committees for the America Society of Heating, Refrigerating and Air-Conditioning Engineers' (ASHRAE) Standards 12 and the proposed Legionella standard.