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Giardiasis is an infection of the small intestine caused by a microscopic organism (protozoa), Giardia lamblia.

Giardiasis outbreaks can occur in communities in both developed and developing countries where water supplies become contaminated with raw sewage.

It can be contracted by drinking water from lakes or streams where water-dwelling animals such as beavers and muskrats, or domestic animals such as sheep, have caused contamination. It is also spread by direct person-to-person contact, which has caused outbreaks in institutions such as day care centers.

Travelers are at risk for giardiasis throughout the world. Campers and hikers are at risk if they drink untreated water from streams and lakes. Other risk factors include:

• Exposure to a family member with giardiasis
• Institutional (day care or nursing home) exposure
• Unprotected anal sex

• Abdominal pain
• Diarrhea
• Gas or bloating
• Headache
• Loss of appetite
• Low-grade fever
• Nausea
• Swollen or distended abdomen
• Vomiting

The time between being infected and developing symptoms is 7 - 14 days. The acute phase lasts 2 - 4 weeks.

Tests that may be done include:

• Enteroscopy
• Stool antigen test to check for Giardia
• Stool ova and parasites exam
• String test (rarely performed)

This disease may also affect the results of the following tests:

• D-xylose absorption
• Small bowel tissue biopsy
• Smear of duodenal aspirated fluid

Some infections go away on their own. Anti-infective medicines may be used.

Cure rates are generally greater than 80%. Drug resistance may be a factor in treatment failures, sometimes requiring a change in antibiotic therapy.

In pregnant women, treatment should wait until after delivery, because some of the drugs used to treat the infection can be harmful to the unborn baby.

It is common for the infection to go away on its own. However, persistent infections have been reported and need further antibiotic treatment. Some people who have had Giardia infections for a long time continue having symptoms even after the infection has gone.

• Dehydration
• Malabsorption (inadequate absorption of nutrients from the intestinal tract)
• Weight loss

Call your health care provider if:

• Diarrhea or other symptoms last for more than 14 days
• You have blood in the stool
• You are dehydrated

Use a water purification method such as boiling, filtration, or iodine treatment before drinking surface water. Hikers or others who use surface water should consider all sources as potentially contaminated.

Workers in day care centers or institutions should use good handwashing and hygiene techniques when going from child to child or patient to patient.

Safer sexual practices, especially regarding anal sex, may decrease the risk of contracting or spreading giardiasis.

Giardia; Traveler's diarrhea - giardiasis

Garcia LS. Protozoa: intestinal and urogenital amebae, flagellates and ciliates. In: Cohen J, Powderly WG, eds. Infectious Diseases. 2nd ed. New York, NY: Elsevier; 2004: chap 242.

Hill DR. Giardia lamblia. In: Mandell, GL, Bennett, JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2005: chap 277.

Huston CD. Intestinal protozoa. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 8th ed. Philadelphia, Pa: Saunders Elsevier; 2006: chap 106.

Updated by: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; and George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.