关键词：水质 标准 水质标准 隐孢子虫
What Is Cryptosporidium and
Why Is There Concern about Its
Presence in Drinking Water?
Cryptosporidium parvum (C. parvum) is a protozoan parasite
known to infect humans and many animal species. The
infective oocysts of Cryptosporidium are shed in the feces,
and infection can occur by consumption of contaminated
food or water, ingestion of contaminated recreational water,
or through contact with feces of infected persons or
animals. Cryptosporidium is not new, but is has gained recognition,
both because it has become more widespread and
because of evidence that there are potential life-threatening
consequences of infection in the growing population of
immunocompromised persons. 1
This parasite is most often found in surface water,
although ground water can also be contaminated. Studies
have shown that up to 97% of U.S. surface waters may be
contaminated with Cryptosporidium oocysts.2,3 Surface water
becomes contaminated with Cryptosporidium when heavy
rains cause runoff of animal waste or when contaminated
wastewater is discharged by inefficient or improperly
operated wastewater treatment plants. Conventional water
treatment systems are not completely effective in removing
Cryptosporidium , because the organism is resistant to
chlorine and filtration units can allow infectious oocysts to
pass into finished water. 4
What are the Health
Effects of C. parvum Infection?
The number of confirmed cases of cryptosporidiosis
attributable to drinking water contamination is low, largely
because of case underreporting by patients and by physicians.
Studies show that many physicians are unaware of
cryptosporidiosis and unfamiliar with its symptoms, and
consequently, they often do not test for the infection. 5
The largest outbreak in U.S. history occurred in 1993 when
at least 400,000 people in Milwaukee became ill after drinking
municipal water contaminated with C. parvum.6 A total of
54 deaths were attributed to the outbreak, primarily involving
immunocompromised individuals. 7 Seroprevalence studies
indicate that exposure to Cryptosporidium is widespread in
the U.S., although many cases are asymptomatic. 8
In healthy individuals, Cryptosporidium infection generally
results in a self-limiting diarrhea. Infection may result in
gastrointestinal illness after 2 to 10 days with watery diarrhea,
headache, abdominal cramps, nausea, vomiting, and lowgrade
fever. In healthy persons, symptoms normally disappear
within 1 to 2 weeks. However, persons with
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