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Case 6: A Migrant Worker with Abdominal Pain and Diarrhea

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A The clinical manifestations and the modified acid-fast smear of the stool sample are consistent with a diagnosis of cystoisosporiasis. Treatment should be initiated with trimethoprim-sulfamethoxazole (Bactrim, Septra).

This answer is correct. The clinical findings are non-specific, but are consistent with cystoisosporiasis (formerly known as isosporiasis).  The modified acid fast stain shows the characteristic elliptical Cystoisosopora belli oocyst with visible internal sporocysts.  The size of the oocyst (approximately 25 by 15 um) is consistent with C. belli and much too large for the round Cryptosporidium parvum oocyst (4 to 6 um wide). Trimethoprim-sulfamethoxazole is the treatment of choice for cystoisosporiasis.

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