Giardia Infection (Giardiasis)

What is giardiasis?

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

How common is giardiasis?

In Washington State, 400 to 600 cases of giardiasis are reported annually. The most common exposures reported by Washington residents include recreational water exposure and international travel.

Who gets giardiasis?

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

  • 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.
  • People who swallow contaminated water while swimming, especially in lakes, rivers, springs, ponds,
    and streams. Several community-wide outbreaks have been linked to recreational water or drinking water contaminated with Giardia.
  • People who eat uncooked food that contains Giardia organisms.
  • Children in childcare settings.
  • Close contacts (such as those in the same family or in the same household or childcare setting) or caregivers of infected people.
  • International travelers.
  • People exposed to human feces through sexual contact.

How is giardiasis spread?

Anything that comes in contact with feces from infected humans or animals can become contaminated with the Giardia parasite. People become infected when they swallow the parasite. Giardiasis is commonly spread person to person when the ill person does not adequately wash their hands after using the toilet and then contaminates another person’s food or drink. Lastly, Giardia is sometimes found in water or on surfaces, or soil contaminated with the feces from infected humans or animals.

When and for how long is a person able to spread giardiasis?

A person can spread giardiasis as long as organisms are in the stool.

What are the symptoms of giardiasis?

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

  • Diarrhea
  • Gas or flatulence
  • Greasy or foul smelling stools
  • 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.  Symptoms may last 2 to 6 weeks, but can sometimes last longer. Medications can help decrease the amount of time symptoms last.

How soon after an infection do the symptoms appear?

Symptoms of giardiasis can begin between 3 to 25 days after becoming infected, with the average being between 7-10 days.

Does the infection of giardiasis make a person immune?

No. It is possible to contract giardiasis multiple times.

What are the complications associated with giardiasis?

Giardia infection can cause lingering symptoms and complications, especially in infants and children under 5. The most common complications include:

  • Dehydration. Often a result of severe diarrhea, dehydration occurs when the body doesn't have
    enough water to carry out its normal functions.
  • Failure to thrive. Chronic diarrhea from Giardia infection can lead to malnutrition and harm a child’s
    physical and mental development.
  • Lactose intolerance. Many people with Giardia infection develop lactose intolerance — the inability to properly digest milk sugar. The problem may persist long after the infection has cleared, leading to weight loss in some people.

Is there a vaccine for giardiasis?

There is no vaccine to protect against giardiasis.

What can be done to prevent the spread of giardiasis?

Transmission can often be prevented by regular and thorough hand washing.

  • Wash hands thoroughly with soap and water.
    • Before, during, and after preparing food.
    • Before eating food.
    • After using the toilet and before handling or eating food, especially if ill with diarrhea.
    • After changing a diaper or assisting with toileting, even if you are wearing gloves.
    • After touching something that could be contaminated such as a trash can, cleaning cloth, drain, or soil.
    • After handling animals or their toys, leashes, feces, and living areas.
  • Assist or visually supervise young children and others who may need help with hand washing as needed.

Avoid drinking water that might be contaminated.

  • Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds, or streams.
  • Do not swallow recreational water. For more information on recreational water-related illness, visit
    CDC's Healthy Swimming website (
  • Do not drink untreated water or use ice made from untreated water during community-wide outbreaks of disease caused by contaminated drinking water.
  • Do not drink untreated water or use ice made from untreated drinking water in countries where the water supply might be unsafe.

Avoid eating food that may be contaminated.

  • Use safe, uncontaminated water to wash all food that is to be eaten raw.
  • After washing fruits and vegetables, peel them if you plan to eat them raw.
  • Avoid eating raw or uncooked foods when traveling in countries with poor food and water treatment.

Practice safe swimming.

  • Protect others by not swimming if you are ill with diarrhea and for one week after your diarrhea stops. It is especially important that children in diapers do not swim for one week after they have had diarrhea.
  • Shower with soap and water before entering recreational water. Thoroughly wash a child’s bottom with soap and water after they use the toilet or have a diaper change and before they enter the water.
  • Keep Giardia and other germs out of pools, hot tubs, lakes, rivers, the ocean, etc. by taking the following steps:
  1. Take children to the bathroom frequently or check their diapers often.
  2. Change diapers in the bathroom or a diaper-changing area, not by the water.

Is there a treatment for giardiasis?

Giardia infection can be treated by several prescription medications. Contact your healthcare provider.

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