Diagnostic value of Xpert MTB/RIF Ultra for osteoarticular tuberculosis

The diagnosis of osteoarticular tuberculosis (TB) remains challenging and results in under- or over-diagnosis. The aim of the present study was to evaluate performance of the novel next-generation Xpert MTB/RIF Ultra (Xpert Ultra) in comparison to culture and Xpert MTB/RIF (Xpert) for osteoarticular TB diagnosis in high burden settings.

Osteoarticular TB suspected cases were enrolled consecutively during June 2017 to June 2018 at Beijing Chest Hospital and their pus specimens were subjected to smear, culture, Xpert and Xpert Ultra. Drug susceptibility testing (DST) was conducted for all of the recovered isolates. The performances of Xpert Ultra and Xpert were evaluated using composite reference standard (CRS) as gold standard, which included clinical, laboratory, histopathological, radiological and ≥6 months' follow-up data.

In total, 186 patients were recruited, and 132 of them were diagnosed with osteoarticular TB according to CRS. The direct head-to-head performance comparison for M. tuberculosis detection showed that Xpert Ultra (90.91%, 120/132) produced a higher sensitivity than Xpert (78.79%, 104/132, P = 0.006) and culture (39.39%, 52/132, P < 0.001). When Xpert Ultra outcomes were integrated, the percentage of confirmed osteoarticular TB case increased from 84.09% (111/132) to 93.94% (124/132). The specificities of Xpert and Xpert Ultra were 100% (34/34) and 97.06% (33/34), respectively. Both Xpert Ultra and Xpert accurately identified all of the 9 rifampicin (RIF)-resistant and 38 RIF-sensitive cases defined by phenotypic DST. Therefore, Xpert Ultra was 100% concordant with phenotypic DST for the detection of RIF resistance.

Xpert Ultra detected significantly more osteoarticular TB cases than Xpert or culture, making it a useful tool for rapid diagnosis of osteoarticular TB.