Waterborne Disease Outbreaks and the Multi-barrier Approach to Protecting Drinking Water - Global Drinking Water Management and Conservation - page 14

outbreak, Medford flushed its distribution system with chlorinated and filtered river

water, and Talent initiated corrections to their system de ciencies such as equipment

repairs and treatment alterations (Solo-Gabriele and Neumeister 1996 , p. 81).
In January

June of 1992 North Cumbria in England experienced cryptosporid-
iosis, with an undetermined number of cases. A third of the population of 160,000
was supplied with water from Ennerdale Lake, another third was supplied by
Crummock Lake, and the remaining third was supplied by smaller sources (Goh
et al. 2004 , p. 1007). The contamination occurred in Ennerdale Lake and the source
is believed to have been runoff from nearby livestock. The treatment of Ennerdale
Lake entailed only chlorination, and therefore a lack of

-

filtration was the system
failure that allowed the outbreak to spread in North Cumbria.
From November 1992 to February 1993, Warrington England experienced an
outbreak of cryptosporidiosis. There were 47 con

rmed cases and an estimate of
approximately 1,840 people affected by the contaminated water that was supplied to
38,000 people (Bridgman et al. 1995 , p. 557). Only chlorine was used to treat the
groundwater supply. No filtration was applied, which is common for groundwater

sources because of the natural filtration achieved through the soil. The source of this

outbreak is believed to have been agricultural runoff. It is rare to experience
Cryptosporidium contamination in a groundwater supply, but it is believed that
heavy rainfall caused surface water, contaminated from a

field with livestock fecal
matter, to drain into the groundwater. Research suggests that the use of groundwater
sources establishes a low immunity to Cryptosporidium so that a contamination will
create a more severe outbreak than may occur in communities that have higher
immunities from the use of surface water (Frost et al. 1997 , p. 10). The system
failure in this case was determined to be a lack of monitoring of the water supply.
This is likely because of the rarity of Cryptosporidium in groundwater sources, and
therefore monitoring of the pathogen was not a regular practice.
The most signi cant drinking water outbreak of cryptosporidiosis was in

Milwaukee Wisconsin from March to April of 1993. Two water treatment plants
supplying water to Milwaukee used water from Lake Michigan. The southern plant,
that supplied southern and central Milwaukee, became contaminated in April 1993.
This caused its temporary closure until June 1993. During this period the northern
plant was required to supply the entire area (Osewe et al. 1996 , p. 298). Both plants
use conventional treatment of coagulation, flocculation, sedimentation, rapid sand

filtration and chlorination treatment (Solo-Gabriele and Neumeister 1996 , p. 81).
The outbreak caused over 403,000 cases of illness and 100 deaths out of approx-
imately 840,000 people whom the water system supplied at the time. The source of
contamination is believed to have been from cattle runoff and also human sewage
that was carried by tributary rivers (Solo-Gabriele and Neumeister 1996 , p. 78).
Another suggestion, in other research, is that the source was recycled backwash
waters (Rose 1997 , p. 141). The recycling of backwash waters is commonly
practiced to clean

flowing water through in the opposite direction to
remove captured particles of matter, in efforts to conserve water (Rose 1997 ,
p. 142). The Milwaukee outbreak has been the largest reported outbreak, and its

filters by