Giardiasis
Giardiasis is a diarrhea-producing infection of the small intestine caused by the single-celled parasite Giardia lamblia.
Giardiasis occurs worldwide and is the most common parasitic infection of the intestine in the United States. Giardia is a common contaminant of fresh water, including many lakes and streams--even ones that appear clean. Most people acquire the infection from drinking contaminated water, but direct person-to-person transmission of cysts passed in the stool also occurs--typically between children or sex partners. Giardiasis is more common among homosexual men with multiple partners, children in day care centers, and people who have traveled to developing countries. Backpackers and hikers who drink untreated water from streams and lakes are also at risk.
Symptoms and Diagnosis
Some infected people have no symptoms. When symptoms occur, they typically consist of cramps, increased gas (flatulence), and foul-smelling diarrhea. If untreated, the diarrhea may persist for weeks, and the person may not absorb enough nutrients from food, resulting in weight loss.
The symptoms often suggest the diagnosis. Microscopic examination of stool samples or secretions taken from the small intestine may reveal the parasite. Because people who have been infected for a long time tend to excrete the parasites at unpredictable intervals, repeated stool examinations may be needed. A stool antigen test can also confirm infection.
Treatment
Metronidazole taken by mouth is effective against Giardia. Nausea and vomiting develop if people drink alcohol while taking it. Furazolidone is available in liquid form and is given to children. People who live with or have had close contact with an infected person and develop symptoms of giardiasis should consult their doctor to see whether they need to be tested or treated for the disease.
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