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Cryptosporidiosis
is infection with Cryptosporidium.
The primary symptom is watery diarrhea, often with other signs of
GI distress. Illness is typically self-limited in immunocompetent
patients but can be persistent and severe in those with AIDS. Diagnosis
is by identification of the organism or antigen in stool. Treatment,
when necessary, is with nitazoxanide.
Cryptosporidia are coccidian protozoa that replicate in small-bowel epithelial cells. Infective oocysts are shed into the lumen and passed in stool. After ingestion by another vertebrate, the oocyst releases sporozoites that transform into trophozoites in epithelial cells, replicate, and then produce oocysts that are released into the lumen of the intestine to complete the cycle. Thin-walled oocysts are involved in autoinfection.
C. parvum and C. hominis are responsible for most human cases. Infections result from fecally contaminated food or water, direct person-to-person contact, or zoonotic spread. The disease occurs worldwide. More than 400,000 people were affected in a waterborne outbreak in Milwaukee, Wisconsin in 1993. Children, travelers to foreign countries, immunocompromised patients, and medical personnel caring for patients with cryptosporidiosis are at increased risk. Cryptosporidiosis is responsible for up to 0.6 to 7.3% of diarrheal illness in industrialized countries and an even higher percentage in areas with poor sanitation. Outbreaks have occurred in day care centers. Severe, chronic diarrhea due to cryptosporidiosis is a problem in patients with AIDS.
Symptoms and Signs
The incubation period is about 1 wk, and clinical illness occurs in > 80% of infected people. Onset is acute, with profuse watery diarrhea, abdominal cramping, and, less commonly, nausea, anorexia, fever, and malaise. Symptoms generally persist 1 to 2 wk, rarely ≥ 1 mo, and then abate. Fecal excretion of oocysts may continue for several weeks after symptoms have subsided. Asymptomatic shedding of oocysts is common among older children in developing countries.
In the immunocompromised host, onset may be more gradual, but diarrhea can be more severe. Unless the underlying immune defect is corrected, infection can persist, causing profuse intractable diarrhea for life. Fluid losses of > 5 to 10 L/day have been reported in some AIDS patients. The intestine is the most common site of infection in immunocompromised hosts; however, other organs may be involved.
Diagnosis
Identifying the acid-fast oocysts in stool confirms the diagnosis, but conventional methods of stool examination are unreliable. Oocyst excretion is intermittent, and multiple stool samples may be needed. Several concentration techniques increase the yield. Cryptosporidium oocysts can be identified by phase-contrast microscopy or by staining with modified Ziehl-Neelsen or Kinyoun techniques. Immunofluorescence microscopy with fluorescein-labeled monoclonal antibodies allows for greater sensitivity and specificity. Intestinal biopsy can demonstrate Cryptosporidium within epithelial cells. Enzyme-linked immunosorbent assay for fecal Cryptosporidium antigen is more sensitive than microscopic examinations for oocysts.
Treatment
and Prevention
In immunocompetent people, cryptosporidiosis is self-limited. Nitazoxanide is used in children. The recommended dose for children 12 to 47 mo is 100 mg q 12 h for 3 days. For ages 4 to 11 yr, it is 200 mg q 12 h for 3 days. Use in adults is currently being investigated, but a dose of 500 mg bid for 3 days has been used. Treatment failures are common with nitazoxanide in patients with AIDS. Symptoms of cryptosporidiosis have abated after effective highly active antiretroviral therapy in some AIDS patients. Supportive measures, oral and parenteral rehydration, and hyperalimentation are indicated in immunocompromised patients.
Stools of patients with cryptosporidiosis are highly infectious; strict stool precautions should be observed. Special biosafety guidelines have been developed for handling clinical specimens. Boiling water is the most reliable decontamination method; only filters with pore sizes ≤ 1 μm (specified as “absolute 1 micron” or certified by NSF Standard No. 53) remove Cryptosporidium cysts.
Last full review/revision November 2005
Content last modified November 2005
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