John Bartlett, MD


July 23, 2003

In This Article

Cryptosporidiosis Review

Leav BA, Mackay M, Ward HD. Cryptosporidium species: new insights and old challenges. Clin Infect Dis. 2003;36:903-908. Abstract This is a review of cryptosporidiosis from Tufts University in Boston, Massachusetts, with the following points:

  • Epidemiology: Approximately 2% of stool studies submitted for cryptosporidia are positive for this parasite.[42] Persons at greatest risk are patients with poorly controlled HIV infection, organ transplants and primary immunodeficiencies, and those receiving immunosuppressive agents.

  • Transmission: The routes are waterborne (the most common documented form), foodborne (possibly under-appreciated), and person-to-person. In the Milwaukee outbreak, the disease involved about 400,000 of the 1.6 million persons in that area. There is no consensus about the safe limits of cryptosporidium in water supplies. Control methods include prevention of contamination, physical removal, and chemical or physical disinfection. These methods reduce contamination, but do not eliminate it. With regard to food, cryptosporidiosis has been associated with ingestion of apple cider, chicken salad, milk, and food prepared by infected food handlers.[43] It has been associated with raw vegetables in developing countries.[44] Cattle are the most common animal reservoir, but their role in transmission to people is unclear.

  • Pathogenesis: The parasite attaches to and invades intestinal epithelial cells, primarily in the jejunum and terminal ileum. In patients with AIDS, any level of the gastrointestinal tract may be involved. The mechanism for causing diarrhea is unknown.

  • Immune response: Cell-mediated immunity appears to be most important, although there is a prominent humoral response as well.

  • Clinical features: The ID50 is 9-1420 oocysts.[45] The characteristic feature is watery diarrhea that is sometimes accompanied by abdominal pain and occasionally by fever, malaise, nausea, vomiting, and anorexia. The incubation period is about 5 days, but can be up to 2 weeks.

  • Diagnosis: The gold standard is the modified acid-fast or Kinyoun state of stool. Several IFA stains are commercially available, but one of the commercial kits was recently withdrawn due to a large number of false-positive results[46] PCR-based techniques may be used to detect a parasite in environmental samples but are not standardized for routine clinical use.

  • Treatment: There is no effective antimicrobial agent and therefore none has been FDA-approved for this indication.

  • Prevention: Effective measures include extensive hand washing, avoidance of stool contact, avoiding accidental ingestion of water in recreational activities, removal of cryptosporidium from drinking water by boiling for one minute or filtering with a pore size of < 1 micron.


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