EVALUATION OF THE SAFETY AND EFFICACY OF CHLORINE DIOXIDE FOR LEGIONELLA CONTROL IN HOSPITAL WATER SYSTEMS

Chlorine dioxide (ClO2) has been used recently in the U.S. for disinfection of hospital water systems to prevent hospital-acquired Legionnaires' disease. The Environmental Protection Agency Maximum Residual Disinfectant Level for chlorine dioxide is 0.8 mg/L. The EPA Maximum Contaminant Level (EPA MCL) for chlorine dioxide disinfection byproduct-chlorite is 1.0 mg/L. The level of chlorite (ClO2−) generated during continuous chlorine dioxide disinfection of hospital water system has not been well studied. In a 31-month prospective study, we evaluated the efficacy of chlorine dioxide to control LEGIONELLA in a hospital water system and monitored the levels of ClO2 and ClO2−. LEGIONELLA positivity was 60% (12/20) in hot water in August 2003, and was reduced to 10% (2/20) in February 2006. An extended time (18 months) was needed to achieve a significant reduction of LEGIONELLA positivity in hot water due to low chlorine dioxide residual in the hot water system. When ClO2 was injected into the cold water main at 0.5-0.7 mg/L, the mean concentration (mg/L) of ClO2 and ClO2− in cold water samples were 0.42 and 0.28, respectively, while the concentrations in hot water samples were 0.07 and 0.42, respectively. The chlorine dioxide concentration in the hot water was significantly lower than in the cold water (p