Keeping Legionella out of water systems

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.