Xpert MTB/RIF ultra for the diagnosis of tuberculous meningitis: A diagnostic accuracy study from India

Setting: Studies evaluating Xpert MTB/RIF Ultra assay (Xpert Ultra) for diagnosing tuberculous meningitis (TBM) are scarce and have reported contrasting results in comparison to Xpert MTB/RIF assay (Xpert).

Objective: To evaluate the performance of Xpert Ultra in diagnosing TBM and compare it with Xpert and multiplex polymerase chain reaction (MPCR).

Design: Xpert Ultra was performed on 244 cerebrospinal fluid (CSF) samples: 56 definite TBM, 148 probable TBM and 40 non-TBM controls. 105/244 CSF samples were also subjected to Xpert and MPCR (IS6110, MPB64, protein B).

Results: The overall sensitivity of Xpert Ultra in diagnosing TBM from 244 CSF samples was 72.05% (96.42% - definite TBM, 62.83% - probable TBM) with a specificity of 100%. 18 (12.24%) cases [8 definite TBM, 10 probable TBM] were reported rifampicin resistant (Rif^R) by Xpert Ultra and confirmed by rpoB sequencing. 60 (40.81%) cases [9 definite TBM, 51 probable TBM] were reported rifampicin indeterminate (Rif^I) by Xpert Ultra (all trace category), out of which 45 [8 definite, 37 probable) were rifampicin susceptible (Rif^S) and 5 probable cases were Rif^R on rpoB sequencing. Out of 105 CSF samples subjected to all three techniques, TBM was diagnosed in 70.66%, 28% and 88% by Xpert Ultra, Xpert and MPCR, respectively.

Conclusion: Xpert Ultra detected TBM with higher sensitivity than Xpert. Among trace category, constituting 40% of TBM cases, rpoB gene sequencing confirmed 5 Rif^R cases.