DETECTION OF BLASTOCYSTIS IN STOOL SPECIMENS USING PARASITOLOGICAL METHODS AND COMMERCIAL ANTIGEN DETECTION ENZYME-LINKED IMMUNOSORBENT ASSAY: A COMPARATIVE STUDY
Nagwa Mostafa El-Sayed and Maha Mohamed Abdel-Wahab
Parasitology Department, Research Institute of Ophthalmology, Giza- Egypt
Diagnosis of Blastocystis is routinely performed by microscopy, staining or culture. However, these methods are time consuming and rely on an experienced technician and subsequent observation of intact organisms. Recently, a new ELISA assay based on the detection of B. hominis antigen in stool samples is available which do not require the observation of intact organisms. So, the present study was conducted to detect B. hominis in stool specimens using different diagnostic methods; direct smear test, modified trichrome staining and copro-antigen detection ELISA comparing to in vitro culture and the diagnostic performance of these tests was statistically compared. A total of 170 stool samples submitted for parasitological analysis to the family health center in 10th of Ramadan city, El-Sharkyia Governorate–Egypt were evaluated. Our results showed that out of 170 examined stool specimens, Blastocystis was detected in 58 (34.1%) of them. On using culture, 51 (30%) stool specimens were identified as positive for this parasite. While, direct wet mount, trichrome staining, and antigen detection ELISA identified 25 (14.7%), 34 (20%) and 45 (26.5%) samples as positive respectively. Comparing to in vitro culture, coproELISA showed the best diagnostic results for sensitivity (88.2%), specificity (100%), positive predictive value (100%), negative predictive value ( 95.2%) and diagnostic accuracy (96.5%). Followed by trichrome staining with 52.9% sensitivity, 94.1% specificity, 79.4% positive predictive value, 82.3 % negative predictive value and 81.7% diagnostic accuracy. Lastly, direct wet mount with 35.3% sensitivity, 94.1% specificity, 72% positive predictive value, 77.2% negative predictive value and 76.4% diagnostic accuracy. Also, there was a significant increase of B. hominis detection using in vitro culture over wet mount and modified trichrome staining by 64.7% and 47.1% (P<0.001, P<0.05) respectively. While, the difference between culture and ELISA in the detection of positive specimens was not significant (P >0.05). In conclusion, ELISA may be useful alternative to parasitological methods. Also, the combination of different diagnostic techniques might detect a high percentage of positive cases.