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Giardiasis is the most common nonbacterial cause of diarrhea in the United States, affecting an estimated 20 percent of the world's population. The disease is caused by a one-celled parasite called Giardia intestinalis. Symptoms may include abdominal pain and vomiting. The condition is more common in children; however, adults are more prone to chronic cases. Treatment involves medications and staying well hydrated.

What Is Giardiasis?

Giardiasis is an intestinal illness that causes diarrhea. In fact, it is the most common nonbacterial cause of diarrhea in the United States (see Diarrhea Causes). Giardiasis is also one of the most common illnesses worldwide, affecting up to 20 percent of the world's population. Giardiasis is most prevalent in developing countries, where infections are often associated with poor sanitary conditions.
Giardiasis is more common in children than in adults. However, chronic giardiasis is more common in adults.

What Causes It?

Giardiasis is caused by a one-celled, microscopic parasite called Giardia intestinalis (or Giardia lamblia). This parasite was initially named Cercomonas intestinalis and renamed Giardia lamblia in 1915. However, many consider Giardia intestinalis to be the correct name for this parasite.

Transmission of Giardiasis

Giardia is found in:
  • Soil
  • Food
  • Water
  • Surfaces that have been contaminated with feces from infected humans or animals.
Giardiasis transmission can occur by accidentally swallowing the parasite; you cannot become infected with Giardia through contact with blood.
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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