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Key Features

Essentials of Diagnosis


  • Self-limited watery diarrhea lasting 2–3 weeks

  • Abdominal cramps, anorexia, malaise, weight loss

  • Fever is unusual


  • Severe and chronic diarrhea

  • Extraintestinal disease has been reported rarely

General Considerations

  • Causes of coccidiosis

    • Cryptosporidium spp, particularly C parvum and C hominis

    • Isospora belli

    • Cyclospora cayetanensis

    • Sarcocystis species

  • These organisms cause endemic childhood gastroenteritis (particularly in malnourished children in developing countries)

  • Infection is transmitted from person to person or by contaminated drinking or swimming water or food

  • Ingested oocysts release sporozoites that invade and multiply in enterocytes, primarily in the small bowel

  • Coccidian oocysts and microsporidian cysts can remain viable in the environment for years

  • I belli appears to infect only humans

  • Incubation period for I belli is about 1 week


  • The infection occurs worldwide, particularly in the tropics and in regions where hygiene is poor

  • Clustering occurs in households, day care centers, and among sexual partners

Clinical Findings

Symptoms and Signs


  • Causes a self-limited watery diarrhea lasting 2–3 weeks

  • Abdominal cramps, anorexia, malaise, and weight loss

  • Fever is unusual

  • Chronic symptoms may persist for months


  • Causes severe and chronic diarrhea

  • Extraintestinal disease has been reported rarely

Differential Diagnosis

  • C parvum, I belli, S bovihominis, and S suihominis

  • Giardiasis

  • Viral gastroenteritis, eg, rotavirus

  • Other traveler's diarrhea, eg, Escherichia coli

  • Cholera

  • Other causes of diarrhea in AIDS, eg, cytomegalovirus colitis


Laboratory Tests

  • Diagnosis is made by examination of stool wet mounts or after modified acid-fast staining, in which the organism is clearly distinguishable from other parasites

  • Other stains also show the organism

  • Sensitivity of stool evaluation is not high because shedding of oocysts may be intermittent; multiple samples should be examined

Diagnostic Procedures

  • Organism may also be identified in duodenal aspiration or small bowel biopsy specimens



  • Most infections in immunocompetent persons do not require treatment

  • Trimethoprim-sulfamethoxazole

    • 160 mg/800 mg two to four times daily for 10 days

    • Higher doses for patients with AIDS

  • An alternative therapy is pyrimethamine (75 mg orally in four divided doses) with folinic acid (10–25 mg/day orally)

  • Maintenance therapy prevents relapse in persons with persistent immunosuppression

    • Low-dose trimethoprim-sulfamethoxazole (160 mg/800 mg daily or three times per week)

    • Fansidar (1 tablet weekly)


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