Giardiasis, caused by Giardia intestinalis, is the most commonly reported intestinal protozoal infection in the U.S. Infection results from ingestion of cysts in fecally contaminated water or food. Human-to-human transmission via the fecal-oral route is especially common among children in day-care centers and nurseries, institutionalized individuals, and male homosexuals.
Infection with Giardia results in an asymptomatic carrier state, acute self-limited diarrhea, or chronic diarrhea. Asymptomatic infection is most common; these individuals excrete Giardia cysts and are a source for new infections. Most adults with symptoms develop an acute self-limited illness, with watery, foul-smelling stools and abdominal distension. Some individuals develop a chronic diarrhea syndrome with malabsorption and weight loss.
The diagnosis of giardiasis is made by identification of cysts or trophozoites in fecal specimens or of trophozoites in duodenal contents. Chemotherapy with a 5-day course of metronida-zole usually is successful, although therapy may need to be repeated or prolonged. A single dose of tinidazole (tindamax) probably is superior to metronidazole for giardiasis. Paromomycin has been used to treat pregnant women to avoid any possible mutagenic effects of the other drugs. Nitazoxanide and tinidazole are FDA-approved for the treatment of giardiasis in immune-competent adults and children >1 year of age.
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