Efficiency of Direct Microscopy of Stool Samples Using an Antigen-Specific Adhesin Test for Entamoeba Histolytica

Abstract

Background:E. histolytica is among the common causes of acute gastroenteritis. The pathogenic species E. histolyti-ca and the nonpathogenic species E. dispar cannot be mor-phologically differentiated, although correct identification of these protozoans is important for treatment and public health. In many laboratories, the screening of leukocytes, erythrocytes, amoebic cysts, trophozoites and parasite eggs is performed using Native-Lugol's iodine for pre-diagnosis.Aims: In this study, we aimed to investigate the fre-quency of E. histolytica in stool samples collected from 788 patients residing in the Anatolian region of İstanbul who presented with gastrointestinal complaints. We used the information obtained to evaluate the effective-ness of microscopic examinations when used in combi-nation with the E. histolytica adhesin antigen test.Study Design: Retrospective cross-sectional studyMethods: Preparations of stool samples stained with Native-Lugol's iodine were evaluated using the E. his-tolytica adhesin test and examined using standard light microscopy at ×40 magnification. Pearson's Chi-square and Fisher's exact tests were used for statistical analysis. Logistic regression analysis was used for multivariate analysis.Results: Of 788 samples, 38 (4.8%) were positive for E. histolytica adhesin antigens. When evaluated together with the presences of erythrocytes, leukocytes, cysts, and trophozoites, respectively, using logistic regression anal-ysis, leukocyte positivity was significantly higher. The odds ratio of leukocyte positivity increased adhesin test-positivity by 2,530-fold (95% CI=1.01-6.330). Adhesin test-positivity was significant (p=0.047).Conclusion: In line with these findings, the consistency between the presence of cysts and erythrocytes and adhe-sin test-positivity was found to be highly significant, but that of higher levels of leukocytes was found to be dis-cordant. It was concluded that leukocytes and trophozo-ites were easily misjudged using direct microscopy. Al-though microscopic examination of samples stained with Native-Lugol's iodine is a cheap and simple method, the confusion of trophozoites with leukocytes may di-rect the clinician toward an incorrect pre-diagnosis. Be-cause trichrome staining is difficult and time consuming, and results may vary depending on the technician, this method is not preferred in most laboratories. Therefore, an enzyme-linked immunosorbent assay method, which is a more advanced method than polymerase chain reac-tion, should be used to distinguish between E. histolyticaand E. dispar in order to achieve an accurate diagnosis