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What is giardiasis?

Giardiasis is an illness caused by Giardia lamblia, a one-celled, microscopic parasite that lives in the intestines of people and animals. The parasite is passed in the bowel movement of an infected person or animal. During the past 15 years, Giardia lamblia has become recognized as one of the most common causes of waterborne disease in humans in the United States. This parasite is found in every region of the United States and throughout the world.

What are the symptoms of giardiasis?

Diarrhea, abdominal cramps, and nausea are the most common symptoms of giardiasis. These symptoms may lead to weight loss and dehydration. However, not everyone infected has symptoms.

How long after being infected do symptoms appear?

Symptoms usually appear 1-2 weeks after infection with the parasite.

How long will I have symptoms?

In otherwise healthy persons, symptoms may last 4-6 weeks. Occasionally, symptoms last longer.

How can I get giardiasis?

You can become infected after accidentally ingesting (swallowing) the parasite. Giardia may be found in soil, food, water, or on surfaces.

  • By swallowing water contaminated with Giardia. A person can swallow a Giardia cyst, the infectious stage of the parasite, by swallowing water from swimming pools, lakes, rivers, springs, ponds, or streams contaminated with sewage or feces from humans or animals.
  • By eating uncooked food contaminated with Giardia. Thoroughly wash with safe water all vegetables and fruits you plan to eat raw.
  • By accidently swallowing the parasite picked up from surfaces (i.e., toys, bathroom fixtures, changing tables, diaper pails) contaminated with stool from an infected person. Hands become contaminated by not following good handwashing practices, particularly after using the toilet, changing diapers, and before eating.

Who is at risk?

Persons at increased risk for giardiasis include child care workers; diaper-aged children who attend day care centers; international travelers; hikers; campers; and others who drink untreated water from contaminated sources. Several community-wide outbreaks of giardiasis have been linked to drinking municipal water contaminated with Giardia.

What should I do if I think I have giardiasis?

See your health care provider.

How is a Giardia infection diagnosed?

Your health care provider will likely ask you to submit stool samples to see if you have the parasite. Because Giardia can be difficult to diagnose, your health care provider may ask you to submit several stool specimens over several days.

What is the treatment for giardiasis?

Several prescription drugs are available to treat Giardia.

How can I prevent giardiasis?

  • Wash hands with soap and water after using the toilet, changing diapers, and before handling food.
  • Avoid drinking water or eating food that may be contaminated.
  • Wash and peel all raw vegetables and fruits before eating.
  • Avoid drinking water from lakes, rivers, springs, ponds, or streams unless it has been filtered and chemically treated.
  • During community-wide outbreaks caused by contaminated drinking water, boil drinking water for 1 minute to kill the Giardia parasite and make the water safe to drink.
  • When traveling in countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water. Bottled or canned carbonated beverages, seltzers, pasteurized fruit drinks, and steaming hot coffee and tea are safe to drink.
  • If you work in a child care center where you change diapers, be sure to wash your hands thoroughly with soap and warm water after every diaper change, even if you wear gloves.
  • If you or your child has Giardia, avoid swimming in pools for 2 weeks after the diarrhea or loose stools have cleared. Giardia cysts are fairly chlorine resistant and are passed in the stools of infected people for several weeks after they no longer have symptoms.

My water comes from a well; should I have my well water tested?

Consider having your well water tested if you answer yes to the following questions:

Are other members of your family or users of your well water ill?

If yes, your well may be the source of infection.

Is your well located at the bottom of a hill or is it considered shallow?

If so, runoff from rain or flood water may be draining directly into your well causing contamination.

Is your well in a rural area where animals graze?

Well water can become fecally contaminated if animal waste seepage contaminates the ground water. This can occur if your well has cracked casings, is poorly constructed or is too shallow.

Tests specifically for Giardia are expensive, difficult, and usually require hundreds of gallons of water to be pumped through a filter. If you answered yes to the above questions, consider testing your well for fecal coliforms instead of Giardia. Although fecal coliform tests do not specifically test for Giardia, testing will show if your well has fecal contamination. If it does, the water may also be contaminated with Giardia, as well as other harmful bacteria and viruses. Look in your local telephone directory for a laboratory or cooperative extension that offers water testing.

My child was recently diagnosed as having giardiasis, but does not have any diarrhea. My health care provider says treatment is not necessary. Is this true?

In general, the answer supported by the American Academy of Pediatrics is that treatment is not necessary. However, there are a few exceptions. If your child does not have diarrhea, but is having nausea, or is fatigued, losing weight, or has a poor appetite, you and your health care provider may wish to consider treatment. If your child attends a day care center where an outbreak is continuing to occur despite efforts to control it, screening and treatment of children without obvious symptoms may be a good idea. The same is true if several family members are ill, or if a family member is pregnant and therefore not able to take the most effective anti-Giardia medications.

For more information:

  1. Addiss DG, Juranek DD, Spencer HC. Treatment of children with asymptomatic and nondiarrheal Giardia infection. Pediatr Infect Dis J 1991;10:843-6.
  2. Addiss DG, Davis JP, Roberts JM, Mast EE. Epidemiology of giardiasis in Wisconsin. Increasing incidence of reported cases and unexplained seasonal trends. Am J Trop Med Hyg 1992;47:13-9.
  3. Bartlett AV, Englander SJ, Jarvis BA, Ludwig L, Carlson JF, Topping JP. Controlled trial of Giardia lamblia: Control strategies in day care centers. Am J Public Health 1991;81:1001-6.
  4. Kreuter AK, Del Bene VE, Amstey MS. Giardiasis in pregnancy. Am J Obstet Gynecol 1981;40:895-901.
  5. Lengerich EJ, Addiss DG, Juranek DD. Severe giardiasis in the United States. Clin Infect Dis 1994; 18:760-3.
  6. Steketee RW, Reid S, Cheng T, et al. Recurrent outbreaks of giardiasis in a child day care center, Wisconsin. Am J Public Health 1989;79:485-90.


This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health care provider. If you have any questions about the disease described above or think that you may have a parasitic infection, consult a health care provider.

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