What is it? And What Can We Do About it?

This article was obtained from a brochure by Jefferson County Health Department and by conversation with Barbara Martens - RN/Communicable Disease Control Coordinator and Mindi Arris - Environmental Health Specialist who are both with Jefferson County.

Camping and Hiking in the High Country

High-country camping and hiking are popular activities in Colorado. Scenic trails and quiet woodlands cut by sparkling streams are a delight to the senses. But hidden within the seemingly clear waters of most mountain streams are microscopic creatures - giardia - which may cause serious illness if ingested. To protect yourself, know the facts and take proper precautions.

Have you had diarrhea, cramps, nausea, vomiting or fatigue; symptoms which vanish and then reoccur at cyclic intervals? You may have Giardia.

Giardiasis is a protozoal infection of the small intestine. Protozoans are microscopic single cell organisms with complex life cycles. The organisms Giardia lamblia, exists in two stages: the active trophozoite (adult stage) and the dormant cyst. The life cycle is started by ingestion of cysts. In the small intestine, the cysts are transformed to the adult stage. Reproduction is by simple fission. As trophozoite pass through the intestinal tract encystations (changes from the adult form to the cyst form) occurs. The cysts are released to the environment through fecal wastes. The cycle is repeated if an individual ingests the cysts, either rthrough contaminated water or fecal-oral contact (hand to mouth transmission). To prevent fecal-oral contact, the following is suggested.

  1. Careful handwashing before preparing food or putting anything in your mouth.

  2. Careful handwashing after changing diapers, toileting, or cleaning up after pets.

  3. Don't let your dog roam. Dogs that roam often catch Giardia and transmit it to kids and adults.

  4. Diagnosis is by identification of cysts or trophozoite in the feces. (Have your doctor do a stool specimen). In 1990, there were 944 diagnosed cases in Colorado.

Incubation Period

May range from 1-4 weeks from exposure, usually 9-15 days.


Man, beavers, dogs, numerous rodents, possibly other animals. Beavers are the most common animal host. In man, asymptomatic carriers (those without symptoms) are more important in the transmission of disease than those with symptoms.

Factors Common to Outbreaks

  • Consumption of water from streams
  • Out of country travel
  • Use of water system that relies on surface water with disinfection as the only treatment
  • Day Care centers (fecal-oral transmission)
  • Shallow wells near streams

Water Testing

Routine coliform counts are inadequate for the evaluation of the presence of cysts. High volume sampling (HVS) ma be effective but is costly and not practical in routine situations (about $75 if done by Jefferson County).

Control Measures

1. Chlorine not effective - a complicated combination of C1 2 residual, pH, time and temperature is necessary to kill the cysts, and is not considered practical or feasible.

2. The effects of other disinfectants, such as ozone and UV radiation are not well known.

3. Filtration is effective provided the filter pore size is no larger than 1.0 micron. This type of filtration should be implemented for surface sources, infiltration galleries or shallow springs. A larger pore size filter should be used ahead of the finer filter to prevent premature plugging.

4. Boiling water for 10 minutes destroys the cysts.

5. For large water treatment plants, adequate control can be acheieved through a combination of filtration and chemical per-treatment.

Common Misconceptions about Giardiasis

1. "Water in streams is purified after flowing for ½ mile". Giardia cysts are stable in water and do not die off down stream. All mountain streams should be presumed to be contaminated by Giardia cysts.

2. "If a water test for coliform bacteria is safe, I do not have to worry about Giardia". While coliform counts do indicate potential problems, a negative count does not rule out the presence of Giardia cysts.

3. "I had Giardiasis, but it went away by itself". By its very nature symptoms re-occur. See your physician for accurate diagnosis and treatment.

For more information, contact the Jefferson County Health Department at 303-232-6301.