Environmental Engineering Reference
In-Depth Information
In 1974 to 1975, a waterborne outbreak of giardiasis occurred in Rome, New
Yo r k .
64
About 5,357 persons out of a population of 46,000 were affected. The
source of water was an upland surface supply receiving only chlorine - ammonia
treatment, which confirmed the inadequacy of such treatment to inactivate the
Giardia cyst. The coliform history was generally satisfactory. Other early giardia-
sis outbreaks in the United States occurred in Grand County (1973, 1974, 1976)
65
and near Estes Park (1976)
65
, Colorado; Camas, Washington (1976)
66
,
67
;Port-
land, Oregon(presumptive, 1954-55)
68
; Unita Mountains, Utah(1974)
69
; Berlin,
New Hampshire (1976)
70
; and in areas of California and Pennsylvania.
71
Between
1969 and 1976 a total of 18 outbreaks with 6,198 cases were reported. An addi-
tional 5 outbreaks with approximately 1,000 cases were reported in 1977. There
were 42 outbreaks reported with 19,728 cases between 1965 and 1980.
72
Atotal
of more than 90 outbreaks occurred through 1984. Acceptable turbidity and col-
iform tests are important for routine water quality control, but they do not ensure
the absence of
Giardia
or enteric viruses; complete water treatment is necessary.
The reporting of outbreaks of waterborne giardiasis has become more common
in the United States, Canada, and other countries of the world. The source of
the
G. lamblia
cyst is humans, and possibly the beaver, muskrat, and other wild
and domestic animals, probably infected from our waste. The
Giardia
stool pos-
itive rate may range from 1 to 30 percent, depending on age and the indigenous
level of personal hygiene and sanitation, with the higher rate in day care centers
and institutions.
73
Infected individuals may shed 10
6
cysts per gram of stool for
many years. The cyst is resistant to normal chlorination, similar to the cyst of
E. histolytica
. Conventional rapid sand filtration of surface water — including
coagulation, flocculation, and sedimentation, slow sand filtration, and diatoma-
ceous earth filtration followed by disinfection — is considered effective in remov-
ing the
Giardia
cyst.
74
Prolonged protected sedimentation and a filter press using
special cellulose sheets (reverse osmosis) to remove 1-
m-size particles is also
reported to be effective.
75
Pressure sand filtration is not reliable and should not
be used, as the cyst penetrates the filter. Experimental results show that 2.5 mg/l
(free) chlorine for 10 minutes killed all cysts at pH 6 at a water temperature of
60
◦
F(15
◦
C), but 60 minutes was required at pH 7 and 8, and 1.5 mg/l at 77
◦
F
(25
◦
C) in 10 minutes at pH 6, 7, and 8; at 42
◦
F(5
◦
C), 2 mg/l killed or inactivated
all cysts in 10 minutes at pH 7 and in 30 minutes at pH 8.
76
A total chlorine resid-
ual of 6.2 mg/l after 30 minutes at pH 7.9 and 37
◦
F(3
◦
C) also inactivated
G. lam-
blia
. A temperature of 131
◦
F(55
◦
C) will destroy the cyst, but boiling is advised.
Cryptosporidium parvum
(Type 1) and
C. hominis
, are both infectious api-
coplexan protozoan parasites of humans. The first human cases of the disease
were reported in 1976.
77
Infection occurs by the ingestion of oocysts that have
been excreted in the feces and the disease, cryptosporidiosis, is usually spread by
the fecal-oral route, but has also been implicated as the cause of food- and water-
borne illness.
78
The incubation period is in the range of 2 to 14 days.
78
It is still
often overlooked or not identified, contributing to the problem of underreporting
of the disease. However, new molecular and clinical diagnostic tests are in use.
The organism is found in the fecal discharges of humans and many wild and
µ
