Comparative Evaluation of GeneXpert MTB/RIF Ultra and GeneXpert MTB/RIF for Detecting Tuberculosis and Identifying Rifampicin Resistance in Pars Plana Vitrectomy Samples of Patients with Ocular Tuberculosis.

Background: Xpert MTB/RIF Ultra (Ultra) was evaluated for the first time on Ocular tuberculosis (OTB) samples and compared with Xpert.
Methods: Seventy five vitreous fluid samples (3 confirmed OTB, 47 clinically suspected OTB, and 25 controls) were subjected to Ultra, Xpert and Multiplex-PCR and compared against culture, composite reference standard (CRS), and gene sequencing.
Results: The sensitivity of Ultra was 50% in diagnosing OTB (100% against culture and 46.8% against CRS). The overall sensitivity of Xpert and MPCR was 16% and 72%, respectively. Xpert missed three culture-positive cases and MPCR detected additional 11. Ultra and Xpert missed two and four cases of RifR, respectively. A total of 13(59%) cases were reported 'trace' by Ultra in which RifR could not be evaluated.
Conclusion: Ultra outperformed Xpert in diagnosing OTB. The advantage of Ultra's simultaneous RifR detection is lost since the trace bacterial loads in the specimens cause indeterminate results of RifR testing. Abbreviations: OTB: Ocular tuberculosis; Ultra: Xpert MTB/RIF Ultra; Xpert: Xpert MTB/RIF, MPCR: multiplex polymerase chain reaction; NAATs: Nucleic acid amplification tests; MLAMP: multitargeted loop-mediated isothermal amplification; PPV: positive predictive value; NPV: negative predictive value; EPTB: extrapulmonary tuberculosis; VF: vitreous fluid; DNA: deoxyribonucleic acid; ATT: antitubercular therapy; RifR: Rifampicin resistance; RifS: Rifampicin susceptible; RifI: Rifampicin indeterminate.