Photo Rounds

Diarrhea and bloating

A 35-year-old man went to his family physician (FP) complaining of diarrhea, nausea, and abdominal bloating. The patient had been camping in the Rocky Mountains and admitted to drinking some of the mountain water. The FP made the presumptive diagnosis of giardiasis and treated him with metronidazole 250 mg tid for 7 days. A month later, the patient returned, complaining of excessive flatulence and sulfurous belching. An upper endoscopy with duodenal biopsies was performed. (The microscopic examination of the duodenal biopsy is shown.)

What's your diagnosis?


Giardia lamblia trophozoites are seen in the center of this high power view of the duodenal biopsy. The patient had typical symptoms of chronic giardiasis (excessive flatulence and sulfurous belching) that failed to improve on metronidazole. G lamblia cysts are ingested from contaminated water, food, or fomites and travel to the small intestine.

The diagnosis may be made by microscopic identification of cysts or trophozoites in stool or in duodenal fluid or biopsy. Antigen tests and immunofluorescence are also an option.

First-line treatment for giardiasis is metronidazole 250 mg orally tid for 5 to 7 days or tinidazole 2 g orally once. Secondary options include oral albendazole or oral nitazoxanide.

In patients with documented treatment failure with metronidazole, it’s best to use a medication from a different class, such as albendazole or nitazoxanide. Other options include treating with a higher dose of metronidazole for a longer course or using combination therapy. In this case, the gastroenterologist chose to give the patient 2 weeks of metronidazole 250 mg tid with 2 weeks of albendazole 400 mg daily. The patient's symptoms resolved completely.

Photo courtesy of Tom Moore, MD. Text for Photo Rounds Friday courtesy of Richard P. Usatine, MD. This case was adapted from: Chumley H. Intestinal worms and parasites. In: Usatine R, Smith M, Mayeaux EJ, Chumley H, Tysinger J, eds. The Color Atlas of Family Medicine. New York, NY: McGraw-Hill; 2009:916-920.

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