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

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

Risk Factors

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

  • Live in crowded places with poor sanitation
  • Drink untreated water
  • Have low stomach acid or take stomach acide 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



Some people do not have symptoms. Others may have:

  • Loose, watery stools that are foul-smelling
  • Belly pain or cramps
  • Bloating
  • Gas
  • Nausea or vomiting
  • Weight loss

Rarely, it may result in:

  • Mild fever
  • Hives or other rash
  • Swelling of the eyes or joints

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


The doctor will ask about symptoms and past health. Questions will also be asked about housing and travel history. A physical exam will be done. This may be enough to point to an infection. A stool test may also be done.

Others in the home will also need testing.



Medicines will treat the infection. Other options to manage symptoms are:

  • Fluids to prevent dehydration
  • Avoiding milk and milk products for 2 to 6 weeks


To lower the risk of giardiasis:

  • Practice proper handwashing, especially before handling food and after using the bathroom or changing a diaper.
  • Avoid swimming in or drinking contaminated water. Drink bottled water or boil water before drinking.
  • Do not eat food that may be contaminated.
  • Use a barrier during oral anal 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.