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The topic of this summary report is Giardia, Cryptosporidium, and waterborne disease. Giardia and Cryptosporidium are becoming the most widespread intestinal parasites, i.e., disease causing organisms, associated with waterborne disease.

These organisms are not bacteria or viruses, but protozoans with complex life cycles. Outside of the host, the organisms are in a cyst stage, which is much like a seed for a plant or microscopic egg.  The size of the Giardia cyst is approximately 8 to 14 um; whereas, the Cryptosporidium oocysts are usually 4 to 6 microns in diameter.  (Note: 1 micron = 0.001 mm = 0.00004 inches ), which is too small to see with the naked eye. These organisms are reasonable for over 100,000 causes of reported outbreaks of waterborne, since 1979.  These are not new organisms and in fact Van Leeuwenhoek first describe Giardia cysts in 1681, but these organisms have not been identified as disease causing agents until the last two decades.


The Disease:

Upon ingestion, the acids in the stomach cause the cysts or oocysts to begin to ex-cyst ("like hatching an egg") and the organism begins to reproduce in the intestines. As few as 10 Giardia cysts have been shown to cause the disease giardiasis and it is not currently known the minimum number of oocysts need to get the disease cryptosporidiosis.  The disease creates symptoms that mimic other gastrointestinal problems and the common symptoms are persistent diarrhea, weight loss, abdominal cramps, nausea, and dehydration. In general, the symptoms begin within a week after exposure and the acute symptoms can last for up to 2 weeks, but chronic symptoms can last for up to 2 months. With proper treatment and our natural immune system, the diseases are not deadly, but these diseases can be life threatening to AIDS patients, small children, elderly, or someone recovering from major surgery.

Special Note:
If a member of your household is diagnosed with either of these diseases, it is critical that all members of the household be tested. This is recommended because one of the individuals may be a asymptomatic (not showing signs of disease) carrier for these organisms. It is also important to note that the side effects of the drugs used to treat these diseases tend to have symptoms similar to the disease and that some people have reported becoming lactose intolerant after having the disease.

Routes of Transmission:

This disease can not be transmitted via a cut or exposure to blood products. The primary route of transmission is any fecal to oral route. I know the statement "fecal to oral" route seems strange and unlikely, but please read some of the following examples. Waterborne: Drinking water supply becomes contaminated by malfunctioning on-lot wastewater disposal systems or improperly disposed sludge.  Groundwater is not a common route of contamination, but surface water can be a common route.  This is why it is important to Know Your H20? (Hazards in Your Community) and the source of your drinking water  (City water users consumer confidence reports).   Foodborne: Mother was changing the diapers of her infant and returned to canning products for the church picnic and the individual purchasing the last batch of the canned items became sick; this would include any personal contact with fecal material, contaminated soil, or pet hair that contains the cysts.  Sexual route: This is a route of transmission if you engage in anal-oral sex. Overall, the most widespread route of transmission is through the consumption of contaminated or inadequately or improperly treated drinking water.


"Backpacker Disease": Hikers and nature lovers would drink water from this clear, "pure" mountain spring or stream and get the disease Giardiasis. Most surface water sources (streams, creeks, springs, etc) can be consider vulnerable or are contaminated by Giardia cysts and Cryptosporidium oocysts.  Since both people and animals (wild and domestic animals) are carriers, it is impossible to prevent these organisms from getting into a surface water source. Therefore, do not drink untreated surface water or from that spring just is down the road; YOU are putting your family at risk. Groundwater sources are usually not vulnerable to contamination by these organisms, but improperly constructed wells, wells under the direct influence of a surface water source, or a damaged well could cause a problem. An improperly constructed well would permit surface water to enter along the casing or through the pitless adapter. A well under the direct influence of surface water means that the amount or thickness of the loss soil is not an adequate filtration barrier. A damaged well would be a well were the casing is cracked, well cap broken, or pitiless adapter permits water to directly enter the well.



Unlike bacteria, Giardia cysts and Cryptosporidium oocysts are more resistant to conventional water treatment, such as: chlorination and ultraviolet irradiation. The primary reason is that these organisms have a cyst stage that exists outside the host, i.e., you, me, and other animals.  In the cyst stage, a thick cell wall protects the organism from these conventional treatment methods.  Not only does the cyst stage protect the organism during disinfection, this stage also permits the organism to stay "dormant" for many months in stream sediments or other moist environments.

The best strategy to protect a water supply is to use a multiple barrier approach.   For large water systems, this approach uses a combination of controlling land-use within a watershed to prevent degradation of the source water and the second barrier is a properly design and well-operated filtration plant. Therefore, the physical removal, maintaining low finished water turbidity/ particle count, and effective disinfection is a combination of engineering controls that can be an effective treatment method.    

For community water systems, this multiple barrier approach may include: sanitary surveys, risk assessment, water supply vulnerability analysis, land use management and control, zoning and development regulations, watershed management, wellhead and water supply protection zones, watershed and well field monitoring, water pretreatment, water filtration, disinfection, water quality monitoring, and water distribution system monitoring.

For individual water supplies, this would include a comprehensive treatment system that may include: evaluating water source, filtration, disinfection, and possibly reverse osmosis or distillation.  National Sanitation Foundation has approved several point-of-use devices.  Prior to selecting a treatment option, it is advisable to have your water tested.

For workers at restaurants, daycare facilities extra, the multiple barrier approach is also necessary. When working with contaminated material make sure to wear gloves, properly wash and the more important step is to dry your hands (cysts can not survive desiccation), and properly dispose of contaminated materials.

Water Testing:

Usually if a person is concerned with the quality of their water and they contact a commercial laboratory, the laboratory will recommend that the well be tested for total coliform bacteria; this is not the organisms Giardia.  Important Note: If you do have your water tested and found to be negative for total coliform bacteria, this does not guarantee that the water is potable. T he results mean that it is "unlikely that disease causing organisms are present". The actual testing for the presence of these organisms is time consuming and can be very expensive. There are only a few laboratories within the United States that can conduct this analysis. If you have any questions regarding analysis you can contact the WATER RESEARCH CENTER, but we do now facilitate a PCR screening test for Giardia, Cryptosporidium, and 5 other pathogens and a Giardia/Crypto Assessment.   If you are looking to have your water sample tested for bacterial or general water quality, please visit our Outreach Program page.

Private Water Supply is Contaminated ?

If your personal water supply system (well, spring, or stream) is contaminated, the first step is to start boiling all the water you use for consumption (food preparation, drinking, brushing teeth, making ice cubes) or consider purchasing bottled water. The next step is to contact a professional (consultant or public health department) and have them provide you with guidance on how to best PROTECT YOUR FAMILY for your area.

Other Reports are available for FREE.

Free Report # 2- Nitrates in Drinking Water
Free Report # 3- Lead in Drinking Water
Homeowners Guide to Drinking Water Test- What do I test for?
Newest Website - The MTBE Fact Sheet
Newest Website - Arsenic In Groundwater  
Newest Website - Trihalomethanes

Great Books on Giardia

New Approaches for Isolation of Cryptosporidium and Giardia

Giardia and Giardiasis: Biology, Pathogenesis, and Epidemiology
(This is a Great Reference !)

Online Training Resources

 Water, Wastewater, and Stormwater Design, Operation, and Management

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