Xpert MTB/RIF and GenoType MTBDRplus assays for the rapid diagnosis of bone and joint tuberculosis

• Xpert MTB/RIF (Xpert) and GenoType MTBDRplus (MTBDR) assays were evaluated rigorously for the rapid diagnosis of bone and joint tuberculosis (BJTB).
• The sensitivities of Xpert and MTBDR were 82% and 72%, respectively, and the specificities were both 100%.
• Xpert was 100% concordant with drug susceptibility testing for the detection of rifampicin resistance.
• The sensitivity of MTBDR for the detection of rifampicin and isoniazid resistance was 83.3% and 85.7%, respectively.
• With their high sensitivities and short turnaround times, Xpert and MTBDR are feasible for the diagnosis of BJTB.

SummaryBackgroundBone and joint tuberculosis (BJTB) constitutes about 10–20% of the extrapulmonary tuberculosis (EPTB) cases in China. The GenoType MTBDRplus assay (MTBDR) has been endorsed by the World Health Organization (WHO) for the diagnosis of pulmonary TB (PTB), while the Xpert MTB/RIF assay (Xpert) has also been endorsed by the WHO for the diagnosis of both PTB and EPTB. The diagnostic utility of these two techniques for BJTB was investigated prospectively.MethodsSixty pus specimens were obtained from orthopedic patients. Smear, culture, Xpert, and MTBDR assays were performed for each specimen, and MGIT 960-based drug susceptibility testing (DST) was conducted for all of the isolates recovered. The diagnostic efficiency of Xpert and MTBDR was evaluated on the basis of bacteriological examination and the composite reference standard (CRS).ResultsFifty of the 60 patients were considered to have BJTB according to the CRS. The sensitivities of smear, culture, Xpert, and MTBDR were 26% (13/50), 48% (24/50), 82% (41/50), and 72% (36/50) respectively, while the specificities of all of the tests were 100% (10/10). Xpert was 100% concordant with MGIT 960-based DST for the detection of rifampicin resistance. MTBDR had a sensitivity of 83.3% and a specificity of 100% for the detection of rifampicin resistance and a sensitivity of 85.7% and specificity of 100% for the detection of isoniazid resistance.ConclusionWith their high sensitivities, short turnaround times, and ability to diagnose TB and detect drug resistance simultaneously, both Xpert and MTBDR are feasible as diagnostic tools for BJTB in clinical practice.