Big Thompson Watershed NEWS

"Beaver Fever." "Backpacker’s Fever." "Giardia." Whatever name you choose, the end result is the same, and it’s not very pleasant. Giardia is a waterborne pathogen, that is, a disease-causing organism commonly found in the waters of Colorado. On Monday evening, November 13^th, the Big Thompson Watershed Forum hosted a general assembly addressing the occurrence of waterborne pathogens in our area and the concern they have caused the public and the water treatment industry. The presentation was in two parts. The first was a discussion of the giardia microorganism itself, presented by Keith Hancock, Principal Analyst with CH Diagnostics. The second was a review of the city of Greeley’s recent experience with a Giardia scare in their water system, presented by Nancy Koch, Greeley’s Water Resources Manager.

Giardia is a common protozoa that has been linked to numerous waterborne outbreaks. While in the cyst stage, Giardia is like a seed looking for a host. Giardia cysts are very stable, and can remain viable for months in cold, clear water. They can, however, be eliminated by pasteurization, appropriate filtration, and sufficient chlorination over time.

Transmission of the cysts is by fecal-oral contamination. In other words, the cysts are excreted (sometimes into water) by an infected animal, and then are ingested by another animal. Giardia cysts have been found in the feces of humans, beaver, muskrat, mule deer, domestic sheep, cattle, elk, coyotes, dogs, cats, horses, moose and a number of small rodents. Thus, human giardia infection can occur due to the presence of giardia cysts in the water supply, or, more commonly, due to poor personal hygiene.

Giardia is a human parasite that primarily affects the small intestine. Although infection by giardia in some people can go completely undetected, others can experience severe abdominal cramping and diarrhea. It takes ingestion of at least 10 cysts for a human to become ill. The incubation period is about 10 days to two weeks, thus humans will not become symptomatic until about 10 days following ingestion of the Giardia cysts. Giardia can be medically treated upon detection.

Although Giardia cysts are abundant in the rivers and streams of Colorado, our water treatment plants filter and chlorinate to eliminate the problem. Routine testing is performed to ensure that the pathogens are eliminated. Last summer, during a routine test, a single Giardia cyst was detected in the treated water exiting one of Greeley’s water treatment plants into the transmission system. Following is an account of the situation surrounding that discovery.

The City of Greeley has two water treatment plants, and supplies drinking water to about 80,000 people. During routine testing in August, one of the treatment plants was found void of Giardia cysts, but one to two weeks later, the other had a positive test – a single cyst was detected. Due to the required time it takes to receive results of the testing, and the occurrence of a holiday during that lag time, the results were received eight days after the water sample was taken.

Greeley transferred immediately to an alternate water supply, and got to work analyzing the situation. The biggest question was, did the chlorinated water remain in the transmission system long enough to allow the chlorine to kill any Giardia cysts that might have made it through the treatment plant? Since this was a question that would take a while to answer due to the complexity of the situation, Greeley decided to issue a boil order just in case.

Since the tested sample had been drawn eight days earlier; the water supply source had been changed; only a single Giardia cyst was detected; and the water was chlorinated in the transmission pipes, the reality of the situation was that there was probably not a problem at this time. If there had been a problem over the past eight days, it was too late to do anything about it. Time would tell.

There was not a single case of Giardia identified that was attributed to the event. The calculations documented that the transmission time in the system was long enough to have killed any Giardia cysts that might have been present. The filter and filtering process at the water treatment plant have been upgraded. Testing is now done at more frequent intervals. So, wash your hands thoroughly and frequently, and leave the fever to the beavers.