Waterborne Disease Outbreaks and the Multi-barrier Approach to Protecting Drinking Water - Global Drinking Water Management and Conservation - page 18

of chlorine disinfection, and therefore higher concentrations and longer contact
times are required for effective treatment, especially in cold water where resistance
increases further (Betancourt and Rose 2004 , p. 224). Therefore, a reliance on only
chlorine disinfection is ineffective and inadequate against the Giardia pathogen.
Filtration and alternative methods, as with Cryptosporidium, are necessary in order
to prevent outbreaks.
A signi cant early outbreak of Giardia contamination occurred in November

1974 in Rome, New York. The outbreak in the surface water source caused
4,800

s
water supply was from Fish Creek and it is believed that the source of contami-
nation was untreated human waste. At the time of the contamination only chlora-
mine disinfection was used, with no

5,300 cases of illness, in the city of approximately 50,148 people. Rome '

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filtration or sedimentation. Chlorine and
ammonia were added to the water entering the reservoir, which forms chloramine,
and chlorine was added again to the water leaving the reservoir (Shaw et al. 1977 ,
p. 428). Disinfection as the only treatment method is insuf

cient in preventing

outbreaks of giardiasis (Craun 1979 , p. 818).
In September December 1979, an outbreak of giardiasis occurred in Bradford,

Pennsylvania affecting 3,500 people. The treatment system for the surface water
source included chlorination, but not

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filtration. Again, in this case minimum levels
of chlorine were ineffective against the Giardia pathogen. The source of contam-
ination is believed to have been fecal matter from beavers in the watershed. Beavers
are common carriers of Giardia. Inadequate treatment and monitoring is believed to
have caused the spread of the outbreak (Hrudey et al. 2002 , pp. 402, 404). Insuf-

ficient levels of chlorine that were unable to provide a chlorine residual in the
distribution system, the lack of filtration, and the failure to monitor chlorine residual

levels allowed the outbreak to occur. Following the outbreak the municipality built
a treatment plant with

filtration in an effort to prevent future outbreaks.
Another Giardia contamination occurred in December 1985 in the water reservoir
in Pitts eld, Massachusetts. The outbreak caused 3,800 cases of illness among the

population of 50,265 people (Hrudey et al. 2002 , p. 399). The source of contami-
nation is believed to have been fecal matter from infected beavers or muskrats. The
cause of the outbreak was due to water treatment changes at the treatment plant. Prior
to the time of contamination, the city used two surface reservoirs that were chlori-
nated, but not filtered (Kent et al. 1988 , p. 139). During this time a new filtration

system was in the process of being installed on the first reservoir, and so a third

reservoir was brought online to phase out the use of the filtration

was being installed. There was an increase in turbidity in the third reservoir; to make
matters worse, chlorine treatment levels were low during that time because of a
malfunctioning chlorinator. Therefore, the water was extremely vulnerable to con-
tamination because of lack of disinfection and the

first reservoir while

filtration had not yet been
installed. Following the outbreak the system was hyper-chlorinated and

ushed, and

chlorine residual levels and contact times were also increased.
In 1986, Penticton British Columbia experienced a drinking water outbreak of
over 3,000 cases of giardiasis. The mixed water source, of both ground and surface
water, was chlorinated but un ltered. The source of the contamination is believed to