Xpert MTB/RIF-generated cycle-threshold (C T) values have poor clinical utility as a rule-in test for smear positivity (cut-point ≤20.2; sensitivity 32.3%, specificity 97.1%) but moderately good rule-out value (cut-point >31.8; negative predictive value 80.0%). Thus, 20% of individuals with CT values >31.8 were erroneously ruled out as smear-negative. This group had a significantly lower sputum bacillary load relative to correctly classified smear-positive patients (C T ≤ 31.8; P <. 001). These data inform on public health and contact tracing strategies.
Bibliographical noteFunding Information:
Financial support. This work was supported by a European Commission Seventh Framework Programme award (TBSusgent) and the Foundation for Innovative New Diagnostics. G. T. is supported by the European and Developing Countries Clinical Trials Partnership (EDCTP), the ‘Evaluation of multiple novel and emerging technologies for TB diagnosis, in smear-negative and HIV-infected persons, in high burden countries’ (TB-NEAT) study, and the South African National Research Foundation (SA NRF). L. P. is supported by fellowships from the McGill University Health Centre Research Institute and Shastri Indo-Canadian Institute. R. v. Z.-S. and J. P. are supported by a Discovery Foundation Fellowship, a Fogarty International Clinical Research Scholars/Fellows Support Centre National Institutes of Health grant (R24TW007988), SATBAT (J. P.), and the EDCTP. K. D. is supported by the EDCTP (TB-NEAT, Trials of Excellence in Southern Africa (TESA), the South African Department of Science and Technology (SA DST), and the SA NRF (SARChI). Potential conflicts of interest. All authors: No reported conflicts.