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MKSAP Quiz: 10-day history of abdominal cramping, diarrhea

A 36-year-old man is evaluated for a 10-day history of abdominal cramping, diarrhea, malaise, and nausea. Diarrhea is watery without mucus or blood. He recently returned from a trip to Lima, Peru. Following a physical exam and stool assay, what is the most appropriate treatment?


A 36-year-old man is evaluated for a 10-day history of abdominal cramping, diarrhea, malaise, and nausea. Diarrhea is watery without mucus or blood. He returned 2 weeks ago from a 7-day trip to Lima, Peru.

On physical examination, temperature is 37.7 °C (99.9 °F); the remaining vital signs are normal. On abdominal examination, bowel sounds are present with diffuse tenderness to palpation. The abdomen is not distended; no guarding or rebound is noted.

Stool polymerase chain reaction assay is positive for Cyclospora.

Which of the following is the most appropriate treatment?

A. Atovaquone
B. Metronidazole
C. Pyrimethamine
D. Quinacrine
E. Trimethoprim-sulfamethoxazole

Reveal the Answer

MKSAP Answer and Critique

The correct answer is E. Trimethoprim-sulfamethoxazole. This content is available to MKSAP 18 subscribers as Question 42 in the Infectious Disease section. More information about MKSAP is available online.

This patient has travel-associated Cyclospora infection and should be treated with trimethoprim-sulfamethoxazole. Cyclospora protozoan infections are typically acquired after consumption of fecal-contaminated food or water, particularly in countries where the parasite is endemic, such as Peru, Guatemala, Haiti, and Nepal. Cyclospora infections may also be acquired through consumption of fresh produce imported from tropical areas. The incubation period is approximately 1 week (range, 2 days to ≥2 weeks). The clinical presentation usually consists of crampy abdominal pain, anorexia, bloating, decreased appetite, fatigue, flatulence, low-grade fever, malaise, nausea, watery diarrhea, and weight loss. Persons with HIV infection may have more severe symptoms associated with wasting.

Diagnosis can be established microscopically by visualization of oocysts with modified acid-fast staining; fluorescence microscopy can be used as well. Several stool specimens may be required because Cyclospora oocysts may be shed intermittently and at low levels, even in persons with profuse diarrhea. Polymerase chain reaction assays appear to have the greatest sensitivity for the diagnosis of a Cyclospora infection.

The recommended treatment is one double-strength tablet of trimethoprim-sulfamethoxazole taken orally twice daily for 7 to 10 days. The Centers for Disease Control and Prevention states no effective alternative treatments have been identified for persons who are allergic to or cannot tolerate trimethoprim-sulfamethoxazole; observation and symptomatic care is recommended for those patients.

Atovaquone has activity against protozoans such as Pneumocystis jirovecii, Toxoplasma, Plasmodium, and Babesia, but not Cyclospora.

Metronidazole has activity against some protozoans, including Giardia, Entamoeba, and Trichomonas, but not Cyclospora.

Pyrimethamine has activity against protozoans such as Toxoplasma, Pneumocystis jirovecii, and Isospora belli, but not Cyclospora.

Quinacrine can be used to treat Giardia but is not effective against Cyclospora.

Key Point

  • Cyclospora infection is treated with oral trimethoprim-sulfamethoxazole.