Alternative names
Giardiasis; Traveler’s diarrhea - giardiasis

Giardia is an infection of the small intestine caused by a protozoa, Giardia lamblia.

Causes, incidence, and risk factors

Giardia 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 where domestic animals such as sheep, have caused contamination. It is also spread by direct person-to-person contact, which has caused outbreaks in 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 unprotected anal sex, exposure to a family member with giardiasis, and institutional (day-care or nursing home) exposure. There has been an increase in cases in the last few years.


  • diarrhea  
  • abdominal pain  
  • abdominal fullness; a gaseous or bloated sensation  
  • abdomen swollen or distended  
  • nausea  
  • loss of appetite  
  • vomiting  
  • headache  
  • low grade fever

Note: The acute phase lasts 7 to 14 days.

Signs and tests

  • Stool ova and parasites showing Giardia  
  • A positive Giardia EIA antibody test  
  • A small bowel biopsy showing Giardia  
  • A string test showing Giardia (rarely performed)

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

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


Some infections resolve on their own. Anti-infective agents such as metronidazole or quinacrine may be used. Furazolidone is generally used to treat children. Cure rates are generally greater than 80%. Drug resistance may be a factor in treatment failures, sometimes requiring a change in antibiotic therapy.

In pergnant women, treatment should wait until after delivery because none of the drugs used to treat the infection are approved for use in pregnancy.

Expectations (prognosis)
Spontaneous resolution is common, but persistent infections have been reported and require further antibiotic treatment. Some people who have had Giardia infections for a long time are slow to resolve their symptoms even after the infection has gone.


  • dehydration  
  • malabsorption (inadequate absorption of nutrients from the intestinal tract)  
  • weight loss

Calling your health care provider
Call your health care provider if diarrhea or other symptoms persist beyond 14 days, or if blood in the stool or dehydration occur.


Water purification methods such as boiling, filtration, and iodine treatment should be used when surface water is used. Hikers or others using 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.

Johns Hopkins patient information

Last revised: December 7, 2012
by Sharon M. Smith, M.D.

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