Molecular Detection of Extra-pulmonary Tuberculosis by the Automated GeneXpert MTB/RIF Assay: 3-years’ experience in a teaching hospital, Saudi Arabia
Fawzia E. Al Otaibi
Abstract
Background: rapid and accurate diagnosis of extrapulmonary tuberculosis (EPTB) continues to be a challenge. Although
culture remains the most sensitive method for confirmation of TB, the prolonged time required for culture, limit its
contribution to clinical decision making. Our study aims to assess the performance of Xpert MTB/RIF test against smear
and culture-confirmed cases of extrapulmonary TB. Methods: A total, 272 non-respiratory specimens (tissues, 88
(32.4%), pleural fluids, 60 (22.1%), CSF, 48 (17.6), aspirate 36 (13.2), ascetic fluid, 20 (7.4), urine, 8 (2.9), body fluid
and pus 5 (1.8) each, and blood 2 (0.73) submitted to the laboratory for Mycobacteria over two-year period were
comparatively investigated with the molecular-based Gene Xpert MTB/RIF assay system and conventional smear and
solid culture methods. Result: The reliability indices of the Gene Xpert MTB/RIF assay are higher compared to smear.
The overall sensitivity (82.1%) of the Gene Xpert MTB/RIF assay is significantly higher than smear (46.9 %). The
highest Mtb positivity agreement between the Xpert MTB/RIF assay and Mtb culture was found in pus and CSF
specimens (100 % [95% CI, 91.1 % to 100 %]) each, while the lowest Mtb positivity agreement was found in the ascetic
fluids specimens (50% [95% CI, 44% to 58%]). The Area under the curve (AUC) of the Receiver Operator Characteristic
(ROC) curve to assess the accuracy of smear was 0.737 (with 95% CI of 0.600-0.874), whereas the AUC of the ROC
curve for Xpert MTB/RIF was 0.946 (with 95% CI of 0.000-1.00). Conclusion: The Xpert assay showed superior
performance over the conventional smear for the rapid detection of M. tuberculosis, in (EPTB).