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Key Features

Essentials of Diagnosis


  • Watery diarrhea

  • Abdominal pain and cramps

  • Nausea and vomiting

  • Fever

  • Mild illnesses and asymptomatic infection may also be common


  • Chronic diarrhea with frequent foul-smelling stools

  • Malabsorption, weight loss

  • Severe, life-threatening watery diarrhea may be seen

  • Extraintestinal disease

General Considerations

  • Causes of coccidiosis

    • Cryptosporidium spp (eg, C parvum and C hominis)

    • Isospora belli

    • Cyclospora cayetanensis

    • Sarcocystis species

  • Oocysts (coccidiosis) or spores (microsporidiosis) are transmitted

    • From person to person

    • 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

  • Coccidia and microsporidians are generally missed on routine evaluations of stool for ova and parasites because special staining techniques are required for identification

  • Leading cause of recreational water-associated outbreaks of gastroenteritis


  • These infections occur worldwide, particularly in the tropics and in regions where hygiene is poor

  • In developing countries, infection seen primarily in children younger than 5 years

  • In developed countries, most patients are adults

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

  • Outbreaks are of particular concern, as exemplified by the 1993 epidemic in Milwaukee in which 400,000 persons became ill

Clinical Findings

Symptoms and Signs


  • Incubation period appears to be 1–14 days

  • Symptoms resolve rapidly, but can persist for 2 weeks or more

  • Diarrhea is usually watery, with accompanying abdominal pain and cramps, nausea, vomiting, and fever

  • Relapses may follow initial resolution of symptoms

  • Mild illnesses and asymptomatic infection are also common


  • Chronic diarrhea with frequent foul smelling stools

  • Malabsorption

  • Weight loss

  • Severe, life-threatening watery diarrhea may be seen

  • Also causes extraintestinal disease, including

    • Pulmonary infiltrates with dyspnea

    • Biliary tract infection with sclerosing cholangitis and AIDS cholangiopathy

Differential Diagnosis

  • Infection with I belli, C cayetanensis, and S bovihominis

  • Giardiasis

  • Viral gastroenteritis, eg, rotavirus

  • Other traveler's diarrhea, eg, Escherichia coli

  • Cholera

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


  • Typically, stool is without blood or leukocytes

  • Diagnosis is made by detecting the organism in stool using a modified acid-fast stain

    • This technique is relatively insensitive

    • Multiple specimens should be evaluated before ruling out the diagnosis

  • Routine evaluation for ova and parasites typically does not include a modified acid-fast stain, so this must be specifically requested in many laboratories

  • Various ...

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