Giardia Infection (Giardiasis)

Giardiasis is an intestinal illness caused by a microscopic parasite called Giardia lamblia.

You can become infected by drinking water or eating food that is contaminated with the parasite. You can also become sick by touching stool or objects contaminated by stool, and then touching your mouth with unwashed hands. Person-to-person transmission can occur in day care centers or other settings where hand-washing practices are poor. Sexual practices that result in hand or mouth contact with stool can also spread the infection.

Giardiasis occurs more often in children and child care workers, people who travel to areas with poor food or water sanitation, men who have sex with men and those who drink water from sources such as lakes, rivers or streams.


Symptoms include:

  • Mild or severe diarrhea
  • Abdominal cramps
  • Bloating
  • Fatigue

Symptoms usually begin within 10 days after exposure, but the range can be from three to 25 days. In some cases, there are no symptoms at all. Fever is rarely present. Occasionally, chronic diarrhea can develop over several weeks or months, with significant weight loss. In otherwise healthy people, symptoms can last two to six weeks.

Once infected, you can carry and shed the parasite for a few weeks to a few months. Treatment with some medicines may shorten this carrier period.


  • Practice good hand hygiene: Wash hands with soap and warm water before touching food, and after using the toilet or changing diapers, handling animal stool or gardening.
  • Avoid water that may be contaminated: Do not drink water directly from streams, lakes, springs or swimming pools. If you must drink from these sources, boil the water for at least one minute or use a filter with a pore size of one micron or smaller.
  • Avoid food that may be contaminated: Thoroughly wash uncooked fruits and vegetables.
  • Take extra care when traveling: When traveling to countries with poor water treatment or food sanitation, avoid raw fruits and vegetables, unboiled tap water, ice and food from street vendors.
  • Protect yourself and others: If you are infected, do not swim in pools or recreational water for two weeks after the diarrhea stops. Sexual practices that result in hand or mouth contact with stool (anal sex, fingering, rimming) can spread disease. To prevent illness, wash the butt, penis and any sex toys thoroughly with soap and water before and after these activities. A dental dam can also provide protection when rimming.

Diagnosis and Treatment

Health care providers can detect the infection through stool tests.

People with giardiasis should drink plenty of fluids, especially young children and pregnant women. Healthy people usually recover on their own without medication. Medicines for treatment such as metronidazole, tinidazole or nitazoxanide can be prescribed by a health care provider.

Returning to Work or School

Since the Giardia parasite is found in the stool, people should stay home from work, school or child care if they cannot control their bowel movements. That includes infants, young children and people with certain types of disabilities.

Food handlers, health care workers and children in day care must get approval from the Health Department before they can return to work or school. This involves follow-up stool testing.

Additional Resources

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