People get giardiasis when they swallow water or food contaminated with stool from an infected person or animal. Persons most at risk for giardiasis are children and staff at day-care centers and persons who drink untreated water when traveling or camping.
Giardiasis is an infection of the intestine that can cause diarrhea.
Giardiasis is caused by Giardia lamblia , a one-celled, microscopic parasite that lives in the intestines of people and animals. Infected people and animals pass Giardia cysts in their stool. Giardia cysts can survive in the environment in water and food and on surfaces and objects. The Giardia parasite is found in every region of the United States and throughout the world. Giardiasis occurs often in mountainous areas where water supplies from lakes, ponds, or streams have become contaminated with animal droppings or human waste.