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JAMA Patient Page
April 6, 2021


Author Affiliations
  • 1Associate Editor, JAMA Network Open
JAMA. 2021;325(13):1356. doi:10.1001/jama.2020.10289

Giardiasis is an intestinal infection caused by the parasite Giardia that can cause prolonged diarrhea.

Giardiasis, an infectious disease of the intestinal tract, occurs after ingesting Giardia parasite cysts (hard shells containing the parasite). Giardia is passed in the feces, from which it can infect other people or animals. It can survive outside the intestinal tract for weeks or months. Giardiasis occurs around the world and is one of the most common intestinal parasites in North America.


The most common symptoms of giardiasis are diarrhea, greasy stool, stomach cramps, nausea, and dehydration. Some people infected by Giardia do not experience any symptoms.

When symptoms occur, they typically begin 1 to 3 weeks after infection and may last 2 to 6 weeks or longer, particularly in people with compromised immune systems. In people who have chronic diarrhea due to giardiasis, weight loss and bulky stool can also occur. Some people with giardiasis develop lactose intolerance that can persist even after the infection has cleared.

Diagnosis and Treatment

Giardiasis is diagnosed by identifying Giardia in stool. There are a variety of stool sample tests to identify Giardia. Diagnosis is important because there are several effective treatments available.

Most people with normal immune systems recover from infection with plenty of rest and hydration. However, there are several prescription medications available, including metronidazole, tinidazole, and nitazoxanide, among others. Choice of medication may depend on medical history and the condition of the person’s immune system. If such treatment does not work, a specialist may be able to prescribe additional medication and testing. Pregnant women can be treated under the supervision of a clinician. Pregnant women and infants are especially at risk of dehydration, so extra care should be taken to ensure adequate hydration.

Who Is at Risk of Giardiasis?

Infection occurs after swallowing the parasite. Giardiasis is spread by drinking or swallowing water from wells, lakes, and other bodies of water that have not been properly treated, having close contact with someone who has giardiasis, exposure to contaminated feces through sexual contact, eating uncooked food that has been contaminated, or ingesting Giardia after contact with contaminated surfaces such as toys or bathrooms.

Children in day care settings, backpackers and hikers who drink untreated water or do not practice good hygiene, international travelers, and close contacts of people who have giardiasis are at risk of infection.

Preventing Infection

Practice good hand hygiene by washing hands thoroughly with soap and water for at least 20 seconds. If soap and water are not available, alcohol-based sanitizers can be used but are not as effective. Avoid drinking or swallowing untreated water that may be contaminated. Drink bottled water, disinfect water by boiling for at least 1 minute, or use a certified filter effective against Giardia when unsure of water safety. Wash fruits and vegetables with uncontaminated water before eating. Avoid eating raw food that may be contaminated.

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Article Information

Conflict of Interest Disclosures: None reported.

Sources: DuPont HL. Persistent diarrhea: a clinical review. JAMA. 2016;315(24):2712-2723. doi:10.1001/jama.2016.7833

Centers for Disease Control and Prevention. Parasites—Giardia. https://www.cdc.gov/parasites/giardia/general-info.html