Evaluation of enzyme linked immunosorbent assay for stool antigen detection for the diagnosis of cryptosporidiosis among HIV negative immunocompromised patients in a tertiary care hospital of northern India

The diagnosis of cryptosporidiosis among HIV positive patients has been the focus of many studies worldwide. However, there is a paucity of data on HIV negative immunocompromised patients like post-renal transplant recipients and those with haematological malignancies. Stool microscopy, the conventional method of diagnosis, is fraught with difficulties like cumbersome sample processing and subjective interpretation. Enzyme linked immunosorbent assay (ELISA), on the other hand, is quicker and easier. The present study was conducted in a tertiary care and super speciality hospital of north India. Stool specimens from HIV negative immunocompromised patients were subjected to both modified acid fast staining for oocysts of Cryptosporidium and ELISA for detection of Cryptosporidium copro-antigen, over a period of six years. Of the 637 specimens evaluated, 97 (15.23%) samples were positive for Cryptosporidium by both techniques; 25 (3.92%) specimens were positive by ELISA and negative by microscopy, 14 (2.20%) specimens were positive by microscopy but negative by ELISA, while 501 (78.65%) specimens were negative for Cryptosporidium by both techniques. Significant correlation was observed as a measure of agreement (Kappa test value 0.795) between modified ZN stained microscopy and ELISA for the detection of Cryptosporidium oocysts. The sensitivity, specificity, positive and negative predictive value of ELISA, keeping stool microscopy as gold standard were 87.38%, 95.25%, 87.39% and 97.28% respectively. We conclude that ELISA may be used as a reliable substitute for microscopy in setups where the case load is higher or expertise in special staining techniques is not available. The cost of the kit can be justified if the sample load is sufficiently high or if immunocompromised patients form a significant patient population.