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.
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
Most people don’t have symptoms. If they do appear, they may cause:
- Watery diarrhea
- Loose, greasy, foul-smelling stools
- Belly pain or cramps
- Nausea or vomiting
- Weight loss
- 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.
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.
To lower your chances of giardiasis:
Wash your hands often, mainly:
- After using the toilet.
- After changing a diaper.
- Before handling or eating food.
- 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, school, or day care until the infection is gone.
- Use barriers when you have oral sex.
This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.
Edits to original content made by Denver Health.
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Centers for Disease Control and Prevention https://www.cdc.gov
IDSA—Infectious Diseases Society of America http://www.idsociety.org
Canadian Public Health Association https://www.cpha.ca
Health Canada https://www.canada.ca
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Giardiasis. Merck Manual Professional Version website. Available at: https://www.merckmanuals.com/professional/infectious-diseases/intestinal-protozoa-and-microsporidia/giardiasis. Updated February 2017. Accessed May 29, 2018.
Parasites–giardia. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/parasites/giardia. Updated July 22, 2015. Accessed May 29, 2018