Diagnosing osteoarticular tuberculosis and detecting rifampicin resistance: A comparative analysis of Truenat MTB Plus vs GeneXpert Ultra

Setting: Diagnosing osteoarticular tuberculosis (OATB) and detecting drug resistance is a challenge in an endemic country like India. Objective: Truenat MTB Plus assay (TruPlus), a chip-based portable machine, was compared with GeneXpert Ultra (GxUltra) for diagnosing drug-resistant OATB. Design: 115 synovial fluid and pus specimens [22 culture-positive confirmed, 58 culture-negative clinicallysuspected, 35 non-TB controls] processed between 2017 and 2023 were subjected to TruPlus, GxUltra and multiplex-PCR for diagnosing OATB. They were further screened for rifampicin resistance using TruRif chip. The performance was evaluated against composite reference standard, phenotypic drug susceptibility testing and rpoB gene sequencing. Results: TruPlus, GxUltra and MPCR detected 77.5 %, 71.25 %, and 83.75 %, cases of OATB, respectively. TruPlus detected five additional cases missed by GxUltra. The performance of TruPlus was comparable to GxUltra (p = 0.074) and to MPCR (p = 0.074), while performance of GxUltra was significantly inferior to MPCR (p = 0.004). The overall agreement with reference standard was substantial for TruPlus and MPCR and moderate for GxUltra. Both TruRif and GxUltra reported 4 cases as rifampicin resistant. Conclusion: TruPlus along with TruRif offers better sensitivity than GxUltra. Its compact and portable platform allows wider application in peripheral settings, thus making it a pragmatic solution for diagnosing OATB and its drug resistance.