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not proven dangerous in healthy individuals, iodine use should be limited to months, not
years.
Filtration is not a reliable method of removing viruses. Although viral
contamination is currently unlikely in North American alpine surface water, high levels
of viral contamination should be assumed in lowland rivers with towns upstream and in
developing countries. In these areas, halogenation or heat should be used instead of, or in
addition to, filtration.
B. Is Cryptosporidium a sufficient risk to mandate filtration of surface water?
Cryptosporidium is a protozoan, transmitted by the fecal-oral route, that can cause enteric
illness. It produces a hardy oocyst. Waterborne outbreaks have been demonstrated and
the oocysts have been found to be widespread in surface water. Although pathogenicity is
not debated, the epidemiology of infection, specifically the incidence of symptomatic
infection and presence of immunity, is unclear. The problem is that the oocyst is
extremely resistant to halogens.
C. Are waterborne pathogens a significant source of illness for wilderness and foreign
travelers? The major source of traveler's diarrhea is food borne. However, waterborne
outbreaks of most enteric pathogens have been confirmed, and the waterborne route has
been shown to be a major source of giardiasis outbreaks in the United States, especially
from surface water. While the risk of illness from wilderness water in North America
may be small and considered negligible by some, countries without sanitation have a
much higher risk due to high levels of enteric pathogens in surface water.
