Comparative Study of Wheatley's Trichrome Stain and In-vitro Culture against PCR Assay for the Diagnosis of Blastocystis sp. in Stool Samples

BACKGROUND: This study evaluated the performance of routine permanent stain and cultivation method in comparison with polymerase chain reaction assay as the reference technique to detect Blastocystis sp.

METHODS: A cross-sectional study was conducted among aboriginal populations that reside in Pahang, Peninsular Malaysia in Feb to Mar 2015. A total of 359 stool samples were examined using Wheatley's trichrome stain, in-vitro cultivation in Jones' medium and PCR assay. Positive amplicons were subjected to sequencing and phylogenetic analysis.

RESULTS: Fifty-six (15.6%) samples were detected positive with Blastocystis sp. by Wheatley's trichrome stain and 73 (20.3%) by in-vitro culture, while PCR assay detected 71 (19.8%) positive samples. Detection rate of Blastocystis sp. was highest in combination of microscopic techniques (27.9%). The sensitivity and specificity of Wheatley's trichrome staining and in-vitro culture techniques compared to PCR assay were 49.3% (95% CI: 37.2-61.4) and 92.7% (95% CI: 89.1-95.4) and 39.4% (95% CI: 28.0-51.8) and 84.4% (95% CI: 79.7-88.4), respectively. However, the sensitivity [60.6% (95% CI: 48.3-71.9)] of the method increased when both microscopic techniques were performed together. False negative results produced by microscopic techniques were associated with subtype 3. The agreement between Wheatley's trichrome stain, in-vitro culture and combination of microscopic techniques with PCR assay were statistically significant by Kappa statistics (Wheatley's trichrome stain: K = 0.456, P<0.001; in-vitro culture: K = 0.236, P<0.001 and combination techniques: K = 0.353, P<0.001).

CONCLUSION: The combination of microscopic technique is highly recommended to be used as a screening method for the diagnosis of Blastocystis infection either for clinical or epidemiological study to ensure better and accurate diagnosis.