Comparison of methods investigating Giardia intestinalis, Entamoeba histolytica, and Cryptosporidium spp. in stool samples of patients with diarrhea

Background: Intestinal protozoan infections (IPIs), common all over the world, are an important public health problem, especially in developing countries. Different diagnostic methods are used for the diagnosis of causative agents in diarrhea cases. Objective: This study aims to analyze results of direct microscopy, coproantigen detection test, and PCR technique in diagnosis of G. intestinalis, E. histolytica/dispar, and Cryptosporidium spp. in stool samples of patients with diarrhea. Subjects and Methods: Fresh stool samples were collected from 683 patients complaining of diarrhea, and simultaneously examined by direct microscopy, commercial rapid diagnostic tests (RDTs) for detection of coproantigens, and molecularly using PCR technique. Results: The overall detection rate of parasites was 3.7% by direct microscopy, 6.6% by RDTs and 2% by PCR technique. Moderate, and weak fits were recorded between direct microscopy and RDTs results (Kappa=0.46, P<0.001), and between direct microscopy and PCR technique results (Kappa=0.236, P<0.001), respectively. No fit (Kappa=0.108, P=0.001) was recorded between coproantigen detection test and PCR technique results. Conclusion: It was concluded that direct microscopy and RDTs will be the correct approach in the first instance in the suspicion of IPIs. Despite high cost of PCR technique, it should be considered in differentiation between pathogenic and non-pathogenic amoeba, and genotyping of Cryptosporidium spp.