Clinical Features:
Infection with Cryptosporidium sp. results in a wide range of manifestations, from asymptomatic infections to severe, life-threatening illness.  Watery diarrhea is the most frequent symptom, and can be accompanied by dehydration, weight loss, abdominal pain, fever, nausea and vomiting.  In immunocompetent persons, symptoms are usually short lived (1 to 2 weeks); they can be chronic and more severe in immunocompromised patients, especially those with CD4 counts <200/µl.  While the small intestine is the site most commonly affected, symptomatic Cryptosporidium infections have also been found in other organs including other digestive tract organs, the lungs, and possibly conjunctiva.

Laboratory Diagnosis:
Acid-fast staining methods, with or without stool concentration, are most frequently used in clinical laboratories.  For greatest sensitivity and specificity, immunofluorescence microscopy is the method of choice (followed closely by enzyme immunoassays).  Molecular methods are mainly a research tool.

Safety
Oocysts in stool specimens (fresh or in storage media) remain infective for extended periods.  Thus stool specimens should be preserved in 10% buffered formalin or sodium acetate-acetic acid-formalin (SAF) to render oocysts nonviable.  (Contact time with formalin necessary to kill oocysts is not clear; we suggest at least 18 to 24 hours.)  In addition, the usual safety measures for handling potentially infectious material should be adopted.

For more information on safety, visit the Web site of the Centers for Disease Control and Prevention to view biosafety guidelines (http://www.cdc.gov/od/ohs/biosfty/bmbl4/b4af.htm) or the Web site of the Occupational Safety and Health Administration (OSHA) (http://www.osha.gov/).

Specimen processing
Stool specimens may be submitted fresh, preserved in 10% buffered formalin (see above, “Safety”), or suspended in a storage medium composed of aqueous potassium dichromate (2.5% w/v, final concentration).  The use of mercuric chloride-containing preservatives (e.g.,  polyvinyl alcohol, PVA) is not recommended due to incompatibilities with some methodologies and the environmental hazards posed by the disposal of mercury-containing compounds.  Oocyst numbers can be quite variable, even in liquid stools.  Multiple stool samples should be tested before a negative diagnostic interpretation is reported.  To maximize recovery of oocysts, stool samples should be concentrated prior to microscopic examination.  Formalin-ethyl acetate sedimentation is the recommended stool concentration method for clinical laboratories.  Two potential shortcomings of oocyst concentration techniques are:

• Sedimentation methods are generally performed using low speed centrifugation.  Given their small size and mass, cryptosporidial oocysts may become trapped in the ether or ethyl acetate plug and fail to sediment properly.  Increased centrifugation speed or time (500 × g, 10 minutes) may be warranted when attempting to recover cryptosporidial oocysts.
• Resolution of cryptosporidial infections is accompanied by increasing numbers of non-acid-fast, oocyst “ghosts.”  Such oocysts may not float or sediment as expected, giving rise to false-negative results.

Diagnostic findings:

• Microscopy
• Enzyme immunoassays
• Molecular methods
• Bench aids for Cryptosporidium

Antibody detection: There are currently no commercially available serologic assays for the detection of Cryptosporidium-specific antibodies.  However, immunoblots for detecting the 17 and 27 kDa sporozoite antigens associated with recent infection may be useful for epidemiologic investigations.

Treatment:
Rapid loss of fluids because of diarrhea can be managed by fluid and electrolyte replacement.  Infection in healthy, immunocompetent persons is self-limited.  Nitazoxanide has been approved for treatment of diarrhea caused by Cryptosporidium in immunocompetent patients.  Immunocompromised persons and those in poor health are at highest risk for severe illness.  The effectiveness of nitazoxanide in immunosuppressed persons is unclear.  For persons with AIDS, anti-retroviral therapy, which improves immune status, will also reduce oocyst excretion and decrease diarrhea associated with cryptosporidiosis.    See recommendations in the The Medical Letter as well as Guidelines for preventing opportunistic infections among HIV-infected persons --- 2002 (http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5108a1.htm).

Reference

1. Kaplan JE, Masur H, Holmes KK. Guidelines for preventing opportunistic infections among HIV-infected persons. MMWR June 14, 2002; 51(RR08):1-46.
2. Morgan-Ryan UM, Fall A, Ward LA, Hijjawi N, Sulaiman I, Fayer R, et al. Cryptosporidium hominis n. sp. (Apicomplexa: Cryptosporidiidae) from Homo sapiens. J Eukaryot Microbiol 2002;49:433-440.