Keeping Legionella out of water systems

Abstract

Hospitals are often required to perform a supplemental disinfection of their water systems to protect individuals from hospital‐acquired Legionnaires' disease. The authors of this article recently studied one hospital where three cases of hospital‐acquired Legionnaires' disease were detected in less than two years. These cases were linked to Legionella colonization of the hospital's water system. Chlorine dioxide (ClO2) was considered a cost‐effective approach to disinfection given that ClO2 generators could treat the 23 buildings comprising the hospital complex from one central location. The authors evaluated the efficacy of maintaining a residual of 0.5 to 0.8 mg/L of ClO2 for Legionella control in the secondary distribution system of this 437‐bed hospital over a two‐year period. Monthly monitoring showed mean Legionella positivity at hot water outlets and cold building source water areas decreased from 23 to 12% and 9 to 0%, respectively (p< 0.05). ClO2 residuals decreased with increasing distance from the application point and temperature. Mean ClO2 concentrations were lowest in hot water outlets (0.08 mg/L) followed by cold water outlets (0.33 mg/L) and reservoirs (0.68 mg/L). Complete eradication (0% positivity) of Legionella was achieved after 1.75 years, and no cases of Legionnaires' disease were reported during this time.