Diarrhea Home > What Is Giardia?

Giardia intestinalis, a one-celled microscopic parasite, is the most common nonbacterial cause of diarrhea in the United States. Giardia infections are more prevalent in children than in adults, and up to 20 percent of the world's population is infected with Giardia at any given time.
Giardia is found in soil, food, water, or surfaces that have been contaminated with the feces from infected humans or animals. This diarrhea-causing parasite is most widespread in developing countries where infections are associated with poor sanitary conditions.
Giardia can affect anyone, but certain people are more likely to become infected, including:
  • Parents of infected children
  • International travelers
  • People who swallow water from contaminated sources
  • Swimmers who swallow water while swimming in lakes, rivers, ponds, and streams.
(Click Giardia for more detailed information on what Giardia is, as well as how the parasite is transmitted, the available treatment options, and prevention tactics.)
Written by/reviewed by:
Last reviewed by: Arthur Schoenstadt, MD
Last updated/reviewed:
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