In February 2004, the San Francisco Public Utilities Commission [PUC]
changed its residual drinking water disinfectant from chlorine to
monochloramine in order to achieve new disinfectant byproduct standards in
water delivered to its customers. Prior to the conversion, the Centers for
Disease Control [CDC] in Atlanta, Georgia contacted the PUC with a proposal
to study the effect of the new disinfectant on the occurrence of Legionella in
the drinking water distribution system. Other local health agencies were also
interested in this issue, which resulted in a final study team that included
representatives from the State of California Department of Health Services
[DHS], the California Emerging Infections Program [CEIP], and the San
Francisco Department of Public Health [DPH]. Sites in 53 buildings were
sampled six times each: three times before the conversion to
monochloramine and three times after the conversion. Since Legionella
bacteria are known to survive and multiply within biofilms in large buildings
with extensive hot water systems, only buildings that were at least three
stories were eligible for sampling. At each time point, we collected a water
sample from the primary water heater and four paired water and biofilm
samples from sink faucets or showerheads. Temperature, pH, and free and
total chlorine residual were measured at each site. Samples were sent to
CDC for Legionella culture. Laboratory testing was blinded to the identities of
the buildings. Prior to the conversion to monochloramine, 37 (70%) of
sampled buildings were colonized with Legionella on one or more occasion
and 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 samples
were positive. The reduction of Legionella colonization within buildings
suggests that monochloramine provides better residual disinfection than free
chlorine for limiting the growth of these bacteria in hot water systems. Includes abstract only.
| Edition : | Vol. - No. |
| File Size : | 1
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| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 1 |
| Published : | 06/17/2005 |
