Pronounced: gee-ar-dye-a-sis


Giardiasis is a common intestinal infection that is found around the world.

The Intestines

The Intestines
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Causes    TOP

A specific parasite cause the infection. Giardia cysts are a form of the parasite that survive outside of humans and animals. The cysts spread the infection. You can get it by swallowing the cysts. It grows once it gets to the small intestine. It can pass to you from water, food, or stool that have the cysts. Examples include:

  • Eating food, drinking water, or swimming in water that have the cysts
  • Contact with a person's hands contaminated by human or animal stool
  • Oral to anal contact during sex

Giardiasis spreads easily. It takes only 10 cysts to cause infection.

Risk Factors    TOP

Giardiasis is more common in places without proper water or sewage treatment. Places in Asia or South America have the highest infection rates.

Risk is also higher if you:

  • Live in crowded and unsanitary places
  • Drink untreated water
  • Have low stomach acid
  • Take stomach acid reducers
  • Have oral to anal contact during sex
  • Have a weakened immune system
  • Are a day care worker or work in a group setting
  • Recreate in contaminated water sources when camping or hiking

Symptoms    TOP

Most people don’t have symptoms. If they do appear, they may cause:

  • Watery diarrhea
  • Loose, greasy, foul-smelling stools
  • Belly pain or cramps
  • Bloating
  • Gas
  • Nausea or vomiting
  • Weight loss
  • Rarely:
    • Mild fever
    • Hives or other rash
    • Swelling of eyes or joints

If you don’t have symptoms, you can still pass the infection to others.

Diagnosis    TOP

The doctor will ask about your symptoms. You will be asked about your health and travel history. Your answers and a physical exam may point to giardiasis. If needed, you may also have:

  • Stool tests
  • Fluid or tissue samples from the intestines

If you have the infection, others in your household will need testing.

Treatment    TOP

Medicines will treat the infection. Sometimes, the parasite is resistant. This can make you sick longer.

Prevention    TOP

To lower your chances of giardiasis:

Wash your hands often, mainly:

  • After using the toilet.
  • After changing a diaper.
  • Before handling or eating food.

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.

In general:

  • Do not let children with diarrhea go into swimming pools.
  • Keep swimming pools properly chlorinated.
  • Stay home from work, school, or day care until the infection is gone.
  • Use barriers when you have oral sex.


Centers for Disease Control and Prevention
IDSA—Infectious Diseases Society of America


Canadian Public Health Association


Giardiasis. EBSCO DynaMed Plus website. Available at: Updated August 7, 2017. Accessed May 29, 2018.
Giardiasis. Kids Health—Nemours Foundation website. Available at:
...(Click grey area to select URL)
Updated August 2017. Accessed May 29, 2018.
Giardiasis. Merck Manual Professional Version website. Available at: Updated February 2017. Accessed May 29, 2018.
Parasites–giardia. Centers for Disease Control and Prevention website. Available at: Updated July 22, 2015. Accessed May 29, 2018
Last reviewed May 2018 by David L. Horn, MD, FACP
Last Updated: 5/29/2018

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