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Nearly everyone who dares to drink water from the wild knows the risks that come with it. Tiny organisms lurk in untreated water, waiting to wreak havoc on unsuspecting victims. The problem is, there is no consensus on how widespread this issue is, nor is there a clear solution. Outdoor magazines often contain articles that mix accurate information with misinformation about dealing with backcountry drinking water. The issue lies in the fact that magazine editors don’t necessarily possess scientific expertise, and the writers who submit articles are only partially informed about the presence of microorganisms in water and their proper removal.

The information presented in this report has been compiled from various online sources, including the websites of the U.S. Center for Disease Control (CDC) and the U.S. Food & Drug Administration (FDA). Additional sources, credited at the end of this report, have also been consulted. I have strived to present an unbiased account based on the information I have read and my practical experience, which includes a Forestry degree from the University of Idaho with a minor in Biology. My inspiration for this report comes from an exceptional article titled “What’s in the Water?” by Mark Jenkins, published in the December 1996 issue of Backpacker. That article set a high standard for journalism in outdoor magazines when it comes to addressing issues related to outdoor water. However, given the changes that have occurred in the past 13 years, a new report on “What’s in the Water” is necessary. This report is my well-researched attempt to supplement and update Mark Jenkins’ original piece.

There are three main categories of microorganisms that cause waterborne diseases: Protozoa, Bacteria, and Viruses. Among these, Protozoa are the most prevalent disease-causing microorganisms in backcountry water. They are also the largest and easiest to remove using microfiltration, but they are the most resistant to chemical treatments.

When articles discuss microorganisms in backcountry water, they often highlight two types of Protozoa: Giardia and Cryptosporidium. Both of these Protozoa are widespread, both globally and in North America. A study conducted in 1992 found that 97% of rivers and lakes in the United States contain one or both of these Protozoa. They are present in the intestines of various mammal species, including a significant percentage of humans. Archaeological evidence reveals that Native Americans carried both Giardia and Cryptosporidium over 2,000 years ago. Giardia was first observed under a microscope in 1681, originating from human feces.

The prevalence of Giardia in human stool samples ranges from 2% to 5% in industrialized countries, and from 20% to 30% in developing countries. Severe Giardiasis, the disease caused by Giardia, and its complications resulted in an estimated 4,600 hospitalizations per year between 1979 and 1988 in the United States. According to the CDC, Giardia was responsible for 16.2% of reported drinking-water associated outbreaks of gastroenteritis with a known or suspected infectious cause from 1991 to 2000.

Cryptosporidium may be just as prevalent as Giardia. Surveys indicate that approximately 2% of the North American population carries Cryptosporidium. In 1991, two studies found Cryptosporidium present in 65% to 87% of U.S. surface-water samples.

One challenge with identifying Protozoa infections is their long incubation period, which means that symptoms may only appear 5 to 28 days after drinking untreated water, making it difficult to trace the source of the illness.

While both Giardia and Cryptosporidium are relatively common, the symptoms they cause can be severe. The following table shows the symptoms experienced by 205 patients with confirmed cases of cryptosporidiosis during the Milwaukee outbreak:

– Watery diarrhea: 93%
– Abdominal cramps: 84%
– Weight loss (median 10 lbs): 75%
– Fever (median 100.9 F., range: 98.7-104.9 F.): 57%
– Vomiting: 48%

Giardia symptoms are similar to Cryptosporidium symptoms, but generally do not include fever. Less than 4% of Giardia victims remain symptomatic for more than 2 weeks. In those cases, it can develop into a chronic intestinal condition that may last for years and pose a life-threatening risk due to severe weight loss. Giardia usually responds to treatment with various drugs.

Waterborne Protozoa can be removed from water using microfiltration systems like those produced by Katadyn or MSR.

However, it is important to note that recent testing conducted at the University of Arizona has led researchers to discourage the use of iodine tablets for water treatment. They found that iodine disinfection is not effective in inactivating Cryptosporidium oocysts in water. As this organism is present in all surface waters, they recommend using an alternative treatment method before ingestion. Chlorine Dioxide, when used at a concentration of 4 PPM, has been shown to kill Cryptosporidium, but it may take up to 4 hours in cold, dirty water. The most well-known brand of Chlorine Dioxide tablets is Katadyn Micropur.

Until 2005, there was no specific treatment available for Cryptosporidium infections, and patients had to endure several weeks of suffering. However, a drug called Alinia, containing the active ingredient nitazoxanide, is now prescribed for both Cryptosporidium and Giardia infections. Alinia can cure the infections in about a week for a high percentage of those affected.

It’s likely that many avid outdoor enthusiasts have contracted Giardia or Cryptosporidium during past adventures. Another common source of infection is daycare centers during infancy. Some people may have developed resistance to these protozoa after previous infections, while others may carry and transmit these protozoa in their intestines without showing serious symptoms. It is estimated that up to 15% of infected individuals may be asymptomatic carriers.

Entamoeba histololytica, the protozoan that causes amoebic dysentery, is uncommon in North America and unlikely to affect outdoor enthusiasts here. However, in South America, Africa, and Southeast Asia, it is responsible for more deaths than any other parasite except those that cause malaria. One study suggests that up to 12% of the world’s population may be infected with E. histololytica, with 10% of them experiencing clinical symptoms. The most notable incident in the United States was an outbreak at the Chicago World’s Fair in 1933, caused by contaminated drinking water. The outbreak resulted in 1,000 cases and 58 deaths. Since 1988, sporadic cases of amoebic dysentery have been reported in urban areas across the United States.

Other waterborne protozoa that can infect humans include Cyclospora cayetanensis, Isospora belli, and Microsporidia. These protozoa are not commonly tested for or identified, but they can cause severe diarrhea and other more severe symptoms. Cyclospora and Microsporidia are widespread and carried by many animal species, while Isospora belli is believed to solely infect humans and is found in tropical areas worldwide.

Waterborne bacteria that infect humans are the same ones we are warned about when it comes to improperly processed and cooked meat. The mode of transmission is also similar: contamination from animal or human feces.

Those who drink water downstream from areas where livestock, or in some cases, wild animals have defecated, are at risk of contracting these bacteria. In most cases, only a small number of bacteria need to be ingested to cause illness. Some outdoor enthusiasts may have a natural resistance to particular strains of waterborne bacteria, while others may carry these bacteria in their intestines and infect others without experiencing symptoms.
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Ihab Salloum