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Fawcett Memorial Hospital



Giardiasis is a gastrointestinal infection. It is one of the most common parasitic diseases in the world.

Gastrointestinal System
The Intestines
Copyright © Nucleus Medical Media, Inc.


Giardiasis is caused by a specific, tiny parasite. Giardia cysts are a resistant form of the parasite that can survive outside a human or animal body. These cysts cause the spread of this disease. For infection to occur, a person must ingest Giardia cysts by mouth. After cysts are ingested, the parasites start growing and multiplying in the small intestine. Ingesting as few as ten parasitic cysts can cause an infection.

Giardiasis can occur by:

  • Contact with feces containing the parasitic cysts. Infected feces can be:
    • Human
    • Animal such as cats, dogs, beavers, and cows
  • Eating food, drinking water, or swimming in water contaminated by the parasitic cysts
  • Contact with a person's hands that are contaminated with parasite cyst-infected stool

Risk Factors

Giardiasis is more common in young children and older adults. Other factors that increase your chance of giardiasis include:

  • Unsanitary or crowded living conditions
  • Drinking untreated water, such as:
    • Well water
    • Stream or lake water
  • Low stomach acid, often found in:
    • Older adults
    • People on ulcer drugs
  • Oral-anal sex
  • A weakened immune system
  • Working or staying in a daycare center or nursing home
  • International travelers
  • Internationally adopted children, who may have more than one parasitic infection
  • Hikers, campers, and swimmers


Symptoms usually start 5 to 28 days after infection. Not all people who are infected have symptoms. However, all people who are infected can transmit the disease.

Symptoms may include:

  • Diarrhea
  • Loose, greasy, foul-smelling stools
  • Abdominal pain or cramps
  • Bloating
  • Gas
  • Nausea or vomiting
  • Weight loss
  • Rare findings may include:
    • Mild fever
    • Hives or other rash
    • Swelling of eyes or joints


The doctor will ask about your symptoms and medical history. A physical exam will be done.

Your bodily fluids, tissue, and waste products may be tested. This can be done with:

  • Stool tests
  • Fluid or tissue samples taken from the intestine

If you are diagnosed with giardiasis, everyone living in your household should be tested for the infection as well.


Giardiasis is treated with a prescription antiparasitic drug. The medication is usually given for 5 to 10 days.

This condition may be resistant to medications. This may make treatment difficult. It may also mean that you may be sick longer.


To reduce your chances of getting or spreading giardiasis to others:

  • Maintain good personal hygiene.
  • Wash hands several times a day, especially:
    • Before eating or preparing food.
    • After a bowel movement.
    • After changing a diaper.
  • When camping:
    • Bring bottled water for drinking, cooking, and brushing teeth.
    • Purify untreated water before using—boil, filter, or sterilize.
  • Thoroughly wash or peel raw fruits and vegetables before eating.
  • When traveling overseas:
    • Use only bottled water for drinking, cooking, or brushing teeth.
    • Only eat food that is well cooked and served steaming hot.
  • Do not let children with diarrhea go into swimming pools.
  • Keep swimming pools properly chlorinated.
  • Stay home from work until the infection is gone. Keep children home from school or daycare until the infection is gone.

Revision Information

  • Family Doctor—American Academy of Family Physicians

  • National Institute of Allergy and Infectious Diseases

  • The Canadian Association of Gastroenterology

  • Public Health Agency of Canada

  • Adam RD. Biology of Giardia lamblia. Clin Microbiol Rev. 2001;14(3):447-475.

  • Giardiasis. Nemours Kids Health website. Available at: Updated September 2011. Accessed August 14, 2013.

  • Parasites–giardia. Centers for Disease Control and Prevention website. Available at: Updated March 8, 2011. Accessed August 14, 2013.

  • Nash TE. Surface antigenic variation in Giardia lamblia. Mol Microbiol. 2002;45(3):585-590.