Waterborne Disease Outbreaks and the Multi-barrier Approach to Protecting Drinking Water - Global Drinking Water Management and Conservation - page 17

Cryptosporidiosis then occurred in Gwynedd and Anglesey, Wales in November
2005. Lake Cwellyn was the surface water source for the reservoir that supplied
water to approximately 70,000 households. There were 231 cases of illness caused
by this outbreak. At

first, runoff of animal fecal matter was suspected because of
heavy rains prior to the outbreak, but this was not unusual weather for this area. The
source of contamination is believed to have been human sewage that entered the
reservoir from a sewage treatment system. The human strain of Cryptosporidium is
more dominant in the autumn, while the animal strain is more frequent in the spring.
The treatment of the drinking water included pressurized sand filtration and chlori-

nation, but these methods were not designed to be effective against Cryptosporidium.
There was no speci c treatment failure, but action was taken to add more treatment to

the system. UV treatment was installed, and when it was operating effectively, the
boil water advisory was removed (Outbreak Control Team 2006 , p. 7). This is the
largest waterborne outbreak of cryptosporidiosis in Wales. The early issuing of a boil
water advisory on November 25 probably contained this outbreak. Only a small
proportion of the population became infected, and the installation of UV treatment is
a strong preventative measure against future occurrences.
Another outbreak of Cryptosporidium occurred in Galway Ireland in February
2007. The outbreak caused approximately 242 cases of illness in the city of
approximately 72,000 people. Two treatment plants are used to treat the water
supplied from Lough Corrib (a lake) to the city of Galway. One treatment plant was
newer and used coagulation and rapid gravity

filtration, and the second was older

and had no filtration. The water of the two plants is mixed and then distributed to

the consumers. The source of the contamination is believed to have been human
fecal matter, but the source has not been con rmed. Boil water advisories were

issued by four water suppliers that use water from Lough Corrib. Treatment failure
from a lack of

filtration in the second plant is likely to be the cause of the outbreak.
Closures and upgrades have occurred since the outbreak.
Outbreaks of cryptosporidiosis have occurred in both small and large commu-
nities, as shown through the history of drinking water outbreaks. This indicates the
strength and ability of the Cryptosporidium pathogen to overcome standard treat-
ment of water systems of small rural communities, but also urban areas, as seen in
Kelowna, Kitchener/Waterloo, Milwaukee, and Carrollton. System failures, par-
ticularly in the treatment process, are the main contributing factor that allows
outbreaks to occur. Ineffective chlorine treatment, and a lack of or inadequate

filtration for surface water sources are the common elements in the outbreaks of
cryptosporidiosis.

2.2.2 Giardia

Giardia is another common cause of drinking water disease outbreaks. Similar to
Cryptosporidium, Giardia is also a protozoan that causes symptoms of diarrhoea
and abdominal pains (Craun 1979 , p. 819). Giardia is resistant to minimum levels