Crypto-Giardia antigen rapid test versus conventional modified Ziehl-Neelsen acid fast staining method for diagnosis of cryptosporidiosis.

Objective: To evaluate the validity of Crypto-Giardia antigen rapid test (CA-RT) in comparison with the conventional modified Ziehl-Neelsen acid fast (MZN-AF) staining method for the diagnosis of cryptosporidiosis.

Methods: Fifteen preserved stool samples from previously confirmed infections were used as positive controls and 40 stool samples from healthy people were used as negative control. A total of 85 stool samples were collected from suspected patients with cryptosporidiosis over 6 months during the period from January till June, 2011. The study was conducted in the department of parasitology, central laboratory, Alnoor Specialist Hospital, Makkah, Saudi Arabia. All samples were subjected to CA-RT and conventional MZN-AF staining method. Validation parameters including sensitivity (SN), specificity (SP), accuracy index (AI), positive predictive value (PPV), and negative predictive value (NPV) were evaluated for both tests.

Results: Out of 15 positive controls, CA-RT detected 13 (86.7%) while MZN-AF detected 11(73.3%) positive cases. However, CA-RT detected no positive case in 40 normal controls but MZN-AF detected 2(5%) as positive cases. Based on the results, the SN, SP, AI, PPV and NPV were high in CA-RT than MZN-AF staining method, ie., 86.7%vs. 73.3%, 100%vs. 95%, 96.4%vs. 89.1%, 100%vs. 84.6% and 95.2%vs. 90.5%, respectively. Out of a total of 85 suspected specimens, CA-RT detected 7(8.2%) but MZN-AF detected 6(7.1%) cases as positive.

Conclusions: CA-RT immunoassay is more valid and reliable than MZN-AF staining method.