Giardia infection

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Giardia, or giardiasis, is an infection of the small intestine. A tiny parasite called Giardia lamblia causes it.

Alternative Names

Giardia; G. duodenalis; G. intestinalis; Traveler's diarrhea - giardiasis


The giardia parasite lives in soil, food, and water. It may also be found on surfaces that have come into contact with animal or human waste.

You may become infected if you:

  • Are exposed to a family member with giardiasis
  • Drink water from lakes or streams where animals such as beavers and muskrats, or domestic animals such as sheep, have left their waste
  • Eat raw or undercooked food that has been contaminated with the parasite
  • Have direct person-to-person contact in daycare centers, long-term care homes, or nursing homes with people who are infected with the parasite
  • Have unprotected anal sex

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


The time between becoming infected and symptoms is 7 to 14 days.

Diarrhea is the main symptom. Other symptoms include:

Some people who have had a giardia infection for a long time continue having symptoms, even after the infection is gone.

Exams and Tests

Tests that may be done include:


If there are no symptoms or only mild symptoms, no treatment may be needed. Some infections go away on their own within a few weeks.

Medicines may be used for:

  • Severe symptoms or symptoms that do not go away
  • People who work in a daycare center or nursing home, to reduce the spread of disease

Antibiotic treatment is successful for most people. A change in the type of antibiotic will be tried if symptoms do not go away. Side effects from some of the medicines used to treat giardia are:

  • Metallic taste in the mouth
  • Nausea
  • Severe reaction to alcohol

In most pregnant women, treatment should not start until after delivery. Some drugs used to treat the infection can be harmful to the unborn baby.

Possible Complications

These complications can occur:

When to Contact a Medical Professional

Call your health care provider if:

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


Purify all stream, pond, river, lake, or well water before drinking it. Use methods such as boiling, filtration, or iodine treatment.

Workers in daycare centers or institutions should use good handwashing and hygiene techniques when going from child to child or person to person.

Safer sexual practices may decrease the risk for getting or spreading giardiasis. People practicing anal sex should be especially careful.

Peel or wash fresh fruits and vegetables before eating them.


DuPont HL. Approach to the patient with suspected enteric infection. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 283.

Haines CF, Sears CL. Infectious enteritis and proctocolitis and bacterial food poisoning. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease. 10th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 110.

Nash TE, Hill DR. Giardiasis. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 351.

Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 140.

Version Info

  • Last reviewed on 3/13/2016
  • Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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