Giardiasis

(Giardia Infection)

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• What is giardiasis?
• How do you get giardiasis and how is it spread?
• What are the symptoms of giardiasis?
• How long after infection do symptoms appear?
• How long will symptoms last?
• Who is most likely to get giardiasis?
• What should I do if I think I may have giardiasis?
• How is Giardia infection diagnosed?
• What is the treatment for giardiasis?
• My child does not have diarrhea, but was recently diagnosed as having Giardia infection. My health care provider says treatment is not necessary. Is this true?
• If my child or I have been diagnosed with giardiasis, should I worry about spreading the infection to others?
• How can I prevent Giardia infection?
• If my water comes from a well, should I have my well water tested?

What is giardiasis?

Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by a microscopic parasite, Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis). Once a person or animal has been infected with Giardia, the parasite lives in the intestine and is passed in feces. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for long periods of time (i.e., months).

During the past 2 decades, Giardia infection has become recognized as a common cause of waterborne disease in humans in the United States. Giardia can be found worldwide and within every region of the United States.

How do you get giardiasis and how is it spread?

The Giardia parasite lives in the intestine of infected humans or animals (e.g., cats, dogs, cattle, deer, and beavers). Millions of germs can be released in a bowel movement of an infected human or animal. Giardia is found on surfaces or in soil, food, or water that has been contaminated with the feces from infected humans or animals. You can become infected after accidentally swallowing the parasite; you cannot become infected through contact with blood. Giardia can be spread by:

• Accidentally swallowing Giardia picked up from surfaces (such as bathroom fixtures, changing tables, diaper pails, or toys) contaminated with feces from an infected person or animal.
• Drinking water or using ice made from contaminated sources (e.g., lakes, streams, shallow [less than 50 feet] or poorly monitored or maintained wells).
• Swallowing recreational water contaminated with Giardia. Recreational water includes water in swimming pools, water parks, hot tubs or spas, fountains, lakes, rivers, springs, ponds, or streams that can be contaminated with feces or sewage from humans or animals.
• Eating uncooked food contaminated with Giardia.
• Having contact with someone who is ill with giardiasis.
• Traveling to countries where giardiasis is common and being exposed to the parasite as described in the bullets above.

What are the symptoms of giardiasis?

Giardia infection can cause a variety of intestinal signs or symptoms, which include

• Diarrhea
• Gas or flatulence
• Greasy stools that tend to float
• Stomach or abdominal cramps
• Upset stomach or nausea

These symptoms may lead to weight loss and dehydration. Some people with Giardia infection have no symptoms at all.

How long after infection do symptoms appear?

Symptoms of giardiasis normally begin 1 to 2 weeks (average 7 days) after becoming infected.

How long will symptoms last?

In otherwise healthy persons, symptoms of giardiasis may last 2 to 6 weeks. Occasionally, symptoms last longer. Medications can help decrease the amount of time symptoms last.

Who is most likely to get giardiasis?

Anyone can get giardiasis. Persons more likely to become infected include

• Children in child care settings, including diaper-aged children.
• Close contacts (such as those in the same family or in the same household or child care setting) or caregivers of infected people.
• People who drink water or use ice made from contaminated sources (e.g., lakes, streams, shallow or poorly monitored or maintained wells). Contaminated water may include water that has not been boiled, filtered, or disinfected with chemicals.
• Backpackers, hikers, and campers who drink untreated or insufficiently treated water or who do not practice good hygiene (e.g., proper hand washing).
• People who swallow contaminated water while swimming, especially in lakes, rivers, springs, ponds, and streams. Several community-wide outbreaks of giardiasis have been linked to recreational water or drinking water contaminated with Giardia.
• International travelers.
• People exposed to human feces through sexual contact.

What should I do if I think I may have giardiasis?

Contact your health care provider.

How is a Giardia infection diagnosed?

Your health care provider will likely ask you to submit stool samples to check for the parasite. Because Giardia can be difficult to diagnose, your provider might ask you to submit multiple stool specimens collected over a few days.

What is the treatment for giardiasis?

Several prescription drugs are available to treat Giardia infection. Although Giardia can infect all people, young children and pregnant women might be more susceptible to dehydration resulting from diarrhea and should, therefore, drink plenty of fluids while ill. Rapid loss of fluids from diarrhea can be especially life threatening to infants. Therefore, parents should talk to their health care providers about fluid replacement therapy options for infants.

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

Treatment is generally not necessary when your child has no symptoms. However, there are a few exceptions. If your child does not have diarrhea, but does have other symptoms such as nausea, fatigue (feels very tired), weight loss, or a poor appetite, you and your health care provider may wish to consider treatment. 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.

If my child or I have been diagnosed with giardiasis, should I worry about spreading the infection to others?

Yes, Giardia infection can be very contagious. Follow these guidelines to avoid spreading Giardia to others:

1. Wash your hands with soap and water after using the toilet and before handling food.
2. Do not swim in recreational water (pools, hot tubs, lakes, rivers, the ocean, etc.) while you have diarrhea and for 1 week after your diarrhea stops. You can pass Giardia in your feces and contaminate the water after your symptoms have stopped. This has resulted in outbreaks of Giardia infection among recreational water users.
3. Avoid fecal exposure during sexual activity. This is especially important while experiencing diarrhea caused by giardiasis.
• Use a barrier during oral-anal sex.
• Wash hands immediately after handling a condom used during anal sex or after touching the anus or rectal area.

If your child is diagnosed with giardiasis, follow these guidelines to help your child avoid spreading Giardia infection to others:

If your child receives child care with other children, work with the child care provider or your local health department to identify steps (e.g., keep your child out of group child care until the giardiasis symptoms resolve) you can take to help stop the other children from becoming infected with Giardia.

How can I prevent a Giardia infection?

Practice good hygiene.

Avoid water that might be contaminated.

1. Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds, and streams.
2. Do not drink untreated water or use ice made from untreated water during community-wide outbreaks of disease caused by contaminated drinking water.
3. Do not swallow recreational water. For more information on recreational water-related illness, visit CDC's Health Swimming website.
4. Do not drink untreated water or use ice made from untreated drinking water in countries where the water supply might be unsafe. For information on traveler's health and giardiasis, visit Chapter 4 in CDC's Yellow Book.

In the United States, nationally distributed brands of bottled or canned carbonated water and soft drinks are safe to drink in terms of Giardia contamination. Commercially packaged non-carbonated soft drinks and fruit juices that do not require refrigeration until after they are opened (those that are stored unrefrigerated on grocery shelves) also are safe.

For information on choosing safe bottled water, see CDC’s Fact Sheet A Guide to Commercially-Bottled Water and Other Beverages.

If you are unable to avoid using or drinking water that might be contaminated, then you can make the water safer to drink by doing one of the following:

• Heat the water to a rolling boil for at least 1 minute (at altitudes greater than 6,562 feet [>2,000 meters], boil water for 3 minutes).
  OR
• Use a filter that has an absolute pore size of 1 micron or smaller, or one that has been NSF rated for "cyst removal." For information on choosing a water filter, see CDC's Fact Sheet A Guide to Water Filters.
• If you cannot heat the water to a rolling boil or use a recommended filter, then try chemically treating the water by chlorination or iodination. Using chemicals may be less effective than boiling or filtering because the amount of chemical required to make the water safe is highly dependent on the temperature, pH, and cloudiness of the water.

Avoid food that might be contaminated.

Avoid fecal exposure during sexual activity. This is especially important while experienccing diarrhea caused by giardiasis.

If my water comes from a well, should I have my well water tested?

It depends. You should consider having your well water tested if you can answer “yes” to any of the following questions:

Tests used to specifically identify 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 contamination by testing it for the presence of coliforms or E. coli instead of Giardia. Although tests for fecal coliforms or E. coli do not specifically tell you whether Giardia is present, these tests might show whether your well water has been contaminated by feces. For more information on other germs and chemicals that can contaminate well water, see Contaminants in Well Water.

These tests are only useful if your well is not routinely disinfected with chlorine, since chlorine kills fecal coliforms and E. coli. If the tests are positive, it is possible that the water may also be contaminated with Giardia or other harmful parasites, bacteria and viruses. Contact your local health department or your county cooperative extension service to find out who offers water testing in your area. For information on well testing, see Well Water Testing Frequently Asked Questions. If the fecal coliform test comes back positive, indicating that your well is fecally contaminated, stop drinking the well water and contact your local water authority for instructions on how to disinfect your well.

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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This page last reviewed November 12, 2008

Centers for Disease Control and Prevention
National Center for Zoonotic, Vector-Borne, and Enteric Diseases
Division of Parasitic Diseases