Environmental Engineering Reference
In-Depth Information
4. Children who attend daycare centers, daycare center staff, and par-
ents and siblings of children infected in daycare centers
5. Homosexual men
People in categories 1, 2, and 3 have in common the same general source
of infections; that is, they acquire
Giardia
from fecally contaminated drink-
ing water. The city resident usually becomes infected when the municipal
water treatment process does not include the filter necessary to physically
remove the parasite from the water. The number of people in the United
States at risk (i.e., the number who receive municipal drinking water from
unfiltered surface water) is estimated to be 20 million. International travelers
may also acquire the parasite from improperly treated municipal waters in
cities or villages in other parts of the world, particularly in developing coun-
tries. In Eurasia, only travelers to Leningrad appear to be at increased risk.
In prospective studies, 88% of U.S. and 35% of Finnish travelers to Leningrad
who had negative stool tests for
Giardia
on departure to the Soviet Union
developed symptoms of giardiasis and had positive tests for
Giardia
after
they returned home (Brodsky et al., 1974; Jokipii and Jokipii, 1974). With the
exception of visitors to Leningrad, however,
Giardia
has not been implicated
as a major cause of traveler's diarrhea, as it has been detected in fewer than
2% of travelers who develop diarrhea. Hikers and campers, however, risk
infection every time they drink untreated raw water from a stream or river.
Persons in categories 4 and 5 become exposed through direct contact with
the feces of an infected person, such as the soiled diapers of an infected child
at a daycare center, or through direct or indirect anal-oral sexual practices in
the case of homosexual men.
Although community waterborne outbreaks of giardiasis have received
the greatest publicity in the United States during the past decade, about half
of the
Giardia
cases discussed with staff of the Centers for Disease Control
(CDC) over a 3-year period had a daycare center exposure as the most likely
source of infection. Numerous outbreaks of
Giardia
in daycare centers have
been reported. Infection rates for children in daycare center outbreaks have
ranged from 21 to 44% in the United States and from 8 to 27% in Canada
(Black et al., 1981; Keystone et al., 1978, 1984; Pickering et al., 1981, 1984; Sealy
and Schuman, 1983). The highest infection rates are usually observed in chil-
dren who wear diapers (1 to 3 years of age). In a study of 18 randomly selected
daycare centers in Atlanta (CDC, unpublished data), 10% of diapered chil-
dren were found to be infected. Transmission from this age group to older
children, daycare staff, and household contacts is also common. About 20%
of parents caring for an infected child become infected.
Local health officials and managers of water utility companies need to
realize that sources of
Giardia
infection other than municipal drinking water
exist. Armed with this knowledge, they are less likely to make a quick (and
sometimes wrong) assumption that a cluster of recently diagnosed cases in
