Giardiasis Giardiasis Giardiasis is an illness caused by Giardia lamblia , a one-celled, microscopic parasite that lives in the intestines of people and animals. During the past 15 years, Giardia lamblia has become recognized as one of the most common causes of waterborne disease in humans in the United States. This parasite is found in every region of the United States and throughout the world. Our fact sheet answers some common questions about Giardiasis. Cases with diarrhea are subject to restriction on food handling for the duration of the diarrhea.
Cases are subject to restrictions on day care attendance .