AWWA ACE61814

AWWA ACE61814 Legionella: Impact of Drinking Water Disinfectant Conversion from Chlorine to Monochloramine
Conference Proceeding by American Water Works Association, 06/17/2005

Salerno, J.; Conroy, M.; Jetke, R.; Flannery, B.; Gelling, L.; Weintraub, J.; Vugia, D.

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In February 2004, the San Francisco Public Utilities Commission [PUC]changed its residual drinking water disinfectant from chlorine tomonochloramine in order to achieve new disinfectant byproduct standards inwater delivered to its customers. Prior to the conversion, the Centers forDisease Control [CDC] in Atlanta, Georgia contacted the PUC with a proposalto study the effect of the new disinfectant on the occurrence of Legionella inthe drinking water distribution system. Other local health agencies were alsointerested in this issue, which resulted in a final study team that includedrepresentatives from the State of California Department of Health Services[DHS], the California Emerging Infections Program [CEIP], and the SanFrancisco Department of Public Health [DPH]. Sites in 53 buildings weresampled six times each: three times before the conversion tomonochloramine and three times after the conversion. Since Legionellabacteria are known to survive and multiply within biofilms in large buildingswith extensive hot water systems, only buildings that were at least threestories were eligible for sampling. At each time point, we collected a watersample from the primary water heater and four paired water and biofilmsamples from sink faucets or showerheads. Temperature, pH, and free andtotal chlorine residual were measured at each site. Samples were sent toCDC for Legionella culture. Laboratory testing was blinded to the identities ofthe buildings. Prior to the conversion to monochloramine, 37 (70%) ofsampled buildings were colonized with Legionella on one or more occasionand 347 (24%) of 1,405 samples grew Legionella. After the conversion, 5(9%) of buildings were ever colonized and only 12 (1%) of 1,420 sampleswere positive. The reduction of Legionella colonization within buildingssuggests that monochloramine provides better residual disinfection than freechlorine for limiting the growth of these bacteria in hot water systems. Includes abstract only.