Campers should always treat water from streams and lakes to avoid contracting Giardia, an intestinal parasite.

By Dr. Mae Bixby, Western Montana Clinic

Summer in the mountains brings many of us into the wilderness to explore our beautiful wild spaces. It is important to plan ahead and prepare to avoid illness in the backcountry. This article will review Giardia, the most common intestinal parasite in the United States.

Giardia is a waterborne parasite that causes a diarrheal illness in infected hosts. Giardia is transmitted by ingesting foods or fluids that contain fecal material contaminated by the parasite. Once the parasite is ingested it lives in the intestinal tract and causes abdominal cramping and watery diarrhea. Giardia is often considered a camping or backcountry related illness as it is most commonly transmitted in untreated fresh water such as streams, lakes, wells. However, it can also be found in uncooked foods, contact with someone infected with the parasite, or even from surfaces like changing tables or diapers that are contaminated by feces infected with Giardia. The parasite can survive for several months outside the body, allowing it to spread to new animal hosts once it is ingested.

Giardiasis causes intestinal distress most notably abdominal cramping and a foul smelling diarrhea. It also causes gas, stool that floats, upset stomach, and nausea. A severe illness can lead to significant dehydration especially in children and pregnant women. Symptoms develop 1-3 weeks after exposure and typically last for 2-6 weeks.

Giardia is diagnosed by testing for the parasite in stool samples. Current testing methods are fairly quick and results return in 24 hours or less. However, the parasite is excreted intermittently, so several stool samples obtained on different days is often necessary to confirm the diagnosis. Treatment is with a common antibiotic called metronidazole or Flagyl. This medication reduces symptoms and shortens the length of illness.

Transmission of Giardia can be reduced and potentially prevented by avoiding ingestion of untreated water when swimming in streams and lakes. Campers should take time to treat drinking and cooking water using one of several methods. Giardia can be resistant to chlorine, so treatment methods like iodine drops, boiling, filtering, and steri-pens are recommended. Taking good care to wash one’s hands after going to the bathroom or changing diapers, and always before eating will reduce transmission of Giardia.


“Parasites - Giardia". Centers for Disease Control and Prevention. 22.July.2015. Accessed 11.March.2018.

Perkins, Allen MD, Trimmier, Marirose MD. “Recreational Waterborne Illnesses: Recognition, Treatment, and Prevention”. American Family Physician. 1.May.2017. Accessed 4.March.2018.

Dr. Mae Bixby

Mae Bixby, M.D.