while they may be found in water in the absence of feces, excessive numbers
of coliforms are strong evidence that the water is contaminated with bacteria
from human feces and that microorganisms of human disease are also likely to
be present. Coliform bacteria are easy
to recognize and to count, while the
identication of many separate bacteria in the excretions of people suering
from various diseases would be extremely difcult to isolate and to identify.
Waterbome Viral Diseases.
Since viral diseases can also be disseminated
in the same way, it has been assumed that water free of contamination by in—
testinal bacteria—as measured by the coliform count—would be unlikely to be
dangerously contaminated with viruses. The ratio of viruses to coliforms in
sewage is about 15 to a million [41].
However, in many cases, fewer organisms are needed to cause a viral than
a bacterial infection. For example, in one experiment it was found that 30
percent of human volunteers receiving one polie virus became infected [42],
while a single bacterium is rarely, if ever sufcient to infect. Also, under some
circumstances, viruses can survive in water for longer periods of time than
bacteria.
A virus becomes an important agent in transmitting disease through a wa—
ter supply when it is excreted in urine or feces, is able to survive in water, and
is capable of infecting people when ingested. A number of enteroviruses t
this description. Although all enteroviruses can multiply in the human in—
testinal tract, their effects are not limited to that part of the body. They in—
clude polio viruses which may attack the central nervous system resulting in
paralysis and the coxsackie viruses which may produce a disease similar to
polie and also may produce congenital heart abnormalities in infants. (This
occurs when the uterus of the mother has been infected with the virus.) The
_
enteroviruses also include inuenza—causing viruses and infectious hepatitis.
Approximately 100 viruses may be included in the category of viruses that
could transmit disease through a water supply. Except for infectious hepatitis,
all of these viruses have been isolated and identied and have been found in
human sewage [43].
Evidence for waterborne infectious hepatitis was given in a 1966 report in
the American Journal of Public Health [44]. Infectious hepatitis is a prevalent
viral disease—for example 72,651 cases were reported in 1961. In the journal
report, 48 waterbome outbreaks of infectious hepatitis were analyzed. Of
theSe, 14 outbreaks (29,381 cases) were associated with public water supplies
and 34 outbreaks (1976 cases) With private water supplies. It should be noted
that many of these water supplies had not been chlorinated. The largest re—
cent outbreak of infectious hepatitis occurred from December 1955 to janu—
ary 1956 in New Delhi, India. There the public water source became con—
tamihated with raw sewage. Although the water was subsequently ltered
.
and chlorinated, an epidemic—approximately 28,000 cases—of infectious
hepatitis occurred. There was no increase in typhoid fever or bacterial intestinal diseases during the hepatitis epidemics, however, indicating to water
164 Drinking Water
'
-
of coliforms are strong evidence that the water is contaminated with bacteria
from human feces and that microorganisms of human disease are also likely to
be present. Coliform bacteria are easy
to recognize and to count, while the
identication of many separate bacteria in the excretions of people suering
from various diseases would be extremely difcult to isolate and to identify.
Waterbome Viral Diseases.
Since viral diseases can also be disseminated
in the same way, it has been assumed that water free of contamination by in—
testinal bacteria—as measured by the coliform count—would be unlikely to be
dangerously contaminated with viruses. The ratio of viruses to coliforms in
sewage is about 15 to a million [41].
However, in many cases, fewer organisms are needed to cause a viral than
a bacterial infection. For example, in one experiment it was found that 30
percent of human volunteers receiving one polie virus became infected [42],
while a single bacterium is rarely, if ever sufcient to infect. Also, under some
circumstances, viruses can survive in water for longer periods of time than
bacteria.
A virus becomes an important agent in transmitting disease through a wa—
ter supply when it is excreted in urine or feces, is able to survive in water, and
is capable of infecting people when ingested. A number of enteroviruses t
this description. Although all enteroviruses can multiply in the human in—
testinal tract, their effects are not limited to that part of the body. They in—
clude polio viruses which may attack the central nervous system resulting in
paralysis and the coxsackie viruses which may produce a disease similar to
polie and also may produce congenital heart abnormalities in infants. (This
occurs when the uterus of the mother has been infected with the virus.) The
_
enteroviruses also include inuenza—causing viruses and infectious hepatitis.
Approximately 100 viruses may be included in the category of viruses that
could transmit disease through a water supply. Except for infectious hepatitis,
all of these viruses have been isolated and identied and have been found in
human sewage [43].
Evidence for waterborne infectious hepatitis was given in a 1966 report in
the American Journal of Public Health [44]. Infectious hepatitis is a prevalent
viral disease—for example 72,651 cases were reported in 1961. In the journal
report, 48 waterbome outbreaks of infectious hepatitis were analyzed. Of
theSe, 14 outbreaks (29,381 cases) were associated with public water supplies
and 34 outbreaks (1976 cases) With private water supplies. It should be noted
that many of these water supplies had not been chlorinated. The largest re—
cent outbreak of infectious hepatitis occurred from December 1955 to janu—
ary 1956 in New Delhi, India. There the public water source became con—
tamihated with raw sewage. Although the water was subsequently ltered
.
and chlorinated, an epidemic—approximately 28,000 cases—of infectious
hepatitis occurred. There was no increase in typhoid fever or bacterial intestinal diseases during the hepatitis epidemics, however, indicating to water
164 Drinking Water
'
-