Evaluation of GeneXpert Mycobacterium tuberculosis/Rifampin for the detection of Mycobacterium tuberculosis complex and rifampicin resistance in nonrespiratory clinical specimens

Abstract

Background: The objective of this study is to assess the performance of Xpert Mycobacterium tuberculosis (MTB)/rifampin (RIF), an automated molecular test for MTB and resistance to RIF, against smear microscopy and culture method for the diagnosis of MTB infection.

Methods: This is a retrospective analysis of 168 nonrespiratory patient specimens suspected of tuberculosis (TB) at TB Laboratory of Dubai Health Authority in the United Arab Emirates between September 2016 and November 2018. Each sample underwent smear microscopy, mycobacterial culture, and GeneXpert MTB/RIF test.

Results: Of 168 nonrespiratory samples, 52 samples were positive by both culture and Xpert MTB/RIF, 9 samples were detected positive only by culture. Sensitivity, specificity, positive predictive value, and negative value of the Xpert MTB/RIF test were 82.69%, 100%, 100%, and 92.80%, respectively. No false positive was yielded by the Xpert MTB/RIF, and all 116 samples were true negative by Xpert MTB/RIF. The sensitivity of the Xpert MTB/RIF was 76.92% in lymph node tissue and aspirates, 66.67% in cerebrospinal fluid, 100% in gastric lavage and aspirate, 81.25% in other body fluids, 100% in pus, 85.71% in urine, and 66.67% in other tissue samples. Of 168 strains, five strains were rifampicin resistant by phenotypic and Xpert MTB/RIF and 163 were susceptible to rifampicin with culture and Xpert MTB/RIF.

Conclusion: The performance of Xpert MTB/RIF assay was comparable to the gold standard culture method for identification of MTB in nonrespiratory clinical specimens. It does not replace the gold standard culture method, but it helps to achieve better sensitivity and obtain rapid results within 2 h.

Keywords: Extrapulmonary tuberculosis; GeneXpert Mycobacterium tuberculosis/rifampin; Mycobacterium tuberculosis complex; resistance to rifampicin.