Clinical Information

Giardia lamblia (also known as Giardia duodenalis, Giardia intestinalis) are flagellated protozoa that can be found contaminating natural streams, lakes, and surface water municipal reservoirs. The human host ingests them in water, food, and by the fecal-oral route.

Giardia infect primarily the small intestine causing malodorous watery diarrhea and flatulence after attaching by their ventral sucker. Malabsorption and lactose intolerance may also occur.

Giardiasis is the most common intestinal parasitic infection in the United States and is a common cause of diarrhea in children (especially in day care centers), travelers, and in waterborne epidermics. Although Giardia may be detected using the microscopy-based stool parasitic exam (“ova and parasite exam”), up to 7 specimens may be necessary for optimal sensitivity. Instead, antigen detection using an enzyme-linked immunosorbent assay (ELISA) is a more sensitive method for detection and is therefore a preferred method for detection.

See Parasitic Investigation of Stool Specimens Algorithm and Laboratory Testing for Infectious Causes of Diarrhea in Special Instructions for other diagnostic tests that may be of value in evaluating patients with diarrhea.