During the past 15 years, Giardia lamblia has become recognized as one of the most common waterborne diseases in humans in the United States. Giardia is a tiny parasite that lives in the intestines of people and animals. The parasite is passed in the bowel movement of an infected person or animal. It is found in every region of the United States and throughout the world.

Diaper-aged children who attend day care centers, international travelers, hikers, campers, and others who drink untreated water from contaminated sources, are most at risk for developing infection with Giardia. Several community-wide outbreaks of infection have been linked to drinking municipal water contaminated with Giardia.

People become infected after accidentally swallowing the parasite. Giardia may be found in soil, food, water, or on surfaces.

Some of the ways people can become infected with Giardia include:

  • Eating uncooked food contaminated with Giardia.

  • Swallowing water from swimming pools, lakes, rivers, springs, ponds, or streams contaminated with sewage or feces from humans or animals.

  • Accidentally swallowing the parasite picked up from surfaces contaminated with stool from an infected person, such as toys, bathroom fixtures, changing tables, diaper pails.

The CDC recommends:

  • Washing hands with soap and water after using the toilet, changing diapers, and before handling food.

  • Washing and peeling all raw vegetables and fruits before eating.

  • Avoiding drinking water from lakes, rivers, springs, ponds, or streams unless it has been filtered and chemically treated.

  • Boiling drinking water for one minute to kill the Giardia parasite. This will ensure safe drinking water during community-wide outbreaks caused by contaminated drinking water.

  • When camping or 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 your child has Giardia, avoid swimming in pools for two weeks after the diarrhea or loose stools have cleared. Giardia is fairly chlorine resistant and is passed in the stools of infected people for several weeks after they no longer have symptoms.

For more information or to schedule an appointment, call St. Louis Children's Hospital at 314.454.5437 or 800.678.5437 or email us.