Improved case detection using Xpert <i>Mycobacterium tuberculosis</i>/rifampicin assay in skeletal tuberculosis

Background In India, musculoskeletal tuberculosis (TB) accounts for 10%-25% of extrapulmonary TB. Data on drug-resistant skeletal TB are lacking. At present, the diagnosis is based mainly on radiological techniques. Laboratory confirmation of skeletal TB is delayed as 6-8 weeks are required for culture results. Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay is a fully automated test which simultaneously detects MTB and RIF resistance within 3 h. Hence, this study was done to compare the yield of case detection using Xpert assay in comparison with culture in specimens received from clinically suspected skeletal TB cases. Methods Retrospective analysis of microscopy, culture and Xpert assay results was carried out on specimens received in laboratory from skeletal TB cases from January 2016 to December 2017. Results Of the 201 patients analysed, majority of the specimens were obtained from the spine (55.72%). MTB was detected in 48.68% of tissue and 24% of pus specimens. Xpert assay was detected MTB in 67 (33.33%) specimens of which 53 (47.32%) were from the spine. Culture was detected MTB in 66 (32.83%) specimens. Xpert assay was detected two specimens more than culture. One specimen was positive by only culture. RIF-resistant MTB was detected in 10 (14.92%) specimens by Xpert assay. Conclusion The spine is the most common site involved. Tissue specimen is better for early diagnosis. High RIF resistance in skeletal TB is an alarming situation. Ability of Xpert MTB/RIF assay for rapid and simultaneous detection of MTB and RIF resistance in comparison with culture makes it a useful diagnostic tool in skeletal TB.