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Pronounced: gee-ar-dye-a-sis



Giardiasis is a common infection of the intestines. It is found all around the world.

The Intestines

The Intestines

Copyright © Nucleus Medical Media, Inc.


Causes    TOP

Giardiasis is caused by a parasite. It can easily pass into humans after:

  • Eating food or drinking water that has parasite
  • Swimming in water that has the parasite
  • Contact with a person's hands contaminated by human or animal stool
  • Oral to anal contact during sex

Risk Factors    TOP

Giardiasis is more common in places with poor water or sewage treatment. Asia and South America have the highest infection rates. Risk is also higher for people who:

  • Live in crowded places with poor sanitation
  • 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
  • Swim in water sources that may be contaminated

Symptoms    TOP

Some people do not have signs of illness. Others may have:

  • 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

The infection can pass to others even if symptoms are not present.


Diagnosis    TOP

The doctor will ask about your symptoms. They will ask about housing, health and travel history. The answers and a physical exam may point to an infection. The doctor will often test a sample of your stool to confirm giardiasis.

Others in your home will also need testing.


Treatment    TOP

Medicines will treat the infection.


Prevention    TOP

To lower your chances of giardiasis:

Wash your hands often and always:

  • After use the toilet
  • After change a diaper
  • Before handle or eat food

When camping:

  • Bring bottled water for drinking, cooking, and brushing teeth.
  • Purify untreated water before using. This may mean boil, filter, or sterilize water.
  • 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.

Avoid contact with stool during sex:

  • Use a barrier, such as dental dam, during oral-anal sex.
  • Wash hands after touching a condom used during anal sex.
  • Wash hands after contact with the anal or rectal area.

Treat water in swimming pools as recommended.


Centers for Disease Control and Prevention

IDSA—Infectious Diseases Society of America


Canadian Public Health Association

Health Canada


Giardiasis. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T113949/Giardiasis . Updated June 4, 2018. Accessed September 26, 2019.

Giardiasis. Kids Health—Nemours Foundation website. Available at: https://kidshealth.org/Nemours/en/parents/giardiasis.html. Updated July 2018. Accessed September 26, 2019.

Giardiasis. Merck Manual Professional Version website. Available at: https://www.merckmanuals.com/professional/infectious-diseases/intestinal-protozoa-and-microsporidia/giardiasis. Updated October 2018. Accessed September 26, 2019.

Parasites–giardia. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/parasites/giardia. Updated July 22, 2015. Accessed September 26, 2019.

Dental dam use. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/condomeffectiveness/Dental-dam-use.html. Updated August 12, 2016. Accessed September 26, 2019.

Last reviewed September 2019 by David L. Horn, MD, FACP
Last Updated: 9/26/2019

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