Evaluation of modified Ziehl-Neelsen, direct fluorescent-antibody and PCR assay for detection of Cryptosporidium spp. in children faecal specimens.

Abstract

To determine the sensitivity and specificity of routine screening methods for cryptosporidiosis, three methods including conventional modified Ziehl-Neelsen (MZN), direct fluorescent-antibody (DFA) and Nested-PCR assay compared together. To this end, their ability to identify the low concentrations of Cryptosporidium spp. oocysts in children fecal samples was evaluated. The sample population of this study was children under 12years old who had diarrhea and referred to pediatric hospitals in Tehran, Iran. 2,510 stool specimens from patients with diarrhea were screened for Cryptosporidium oocysts by concentration method and MZN. To determine sensitivity and specificity, Nested-PCR and DFA were performed on 30 positive and 114 negative samples which previously had been proved by MZN. By using the microscopic method, DFA assay and PCR analysis, a total of 30 (1.2%), 28 (1.1%) and 32 (1.27%) positive samples were detected respectively. According to the results, the sensitivity, specificity, and positive and negative predictive values of the Nested-PCR assay were 100%, compared to 94, 100, 100, and 98%, respectively, for MZN and 87.5, 100, 100, and 96%, respectively, for DFA. Results of the present study showed that the Nested-PCR assay was more sensitive than the other two methods and laboratories can use the Nested-PCR method for precise diagnosis of Cryptosporidium spp. However, regarding the costs of Nested-PCR and its unavailability in all laboratories and hospitals, MZN staining on smears has also enough accuracy for Cryptosporidium diagnosis.