Comparison of an indirect fluorescent antibody test and stool examination for the diagnosis of cryptosporidiosis.

A total of 342 patients, 70 with AIDS and 272 without AIDS, who had gastro-intestinal illness were selected for tests for cryptosporidiosis. Stool and serum specimens were obtained from each patient. The stool specimens were examined for cryptosporidial oocysts by acid-fast stain and the serum specimens were tested for specific antibodies against oocysts by an indirect fluorescent antibody (IFA) test. The oocysts were detected in stool specimens of 68 patients (19.8%), whereas specific antibodies were demonstrated in 102 patients (29.8%). The incidence of cryptosporidiosis was 47.1% in AIDS and 12.9% in non-AIDS patients as shown by stool examination, compared to 50% and 24.6% as shown by the IFA test. Based upon the finding of oocysts in stool specimens, the sensitivity and specificity of the IFA test in the diagnosis of cryptosporidiosis was 92.6% and 85.8%, respectively.