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Non-actionable Results, Accuracy, and Effect of First- and Second-line Line Probe Assays for Diagnosing Drug-Resistant Tuberculosis, Including on Smear-Negative Specimens, in a High-Volume Laboratory

2022; Oxford University Press; Volume: 76; Issue: 3 Linguagem: Inglês

10.1093/cid/ciac556

1537-6591

Samantha Pillay, Margaretha de Vos, Brigitta Derendinger, Elizabeth M. Streicher, Tania Dolby, Leeré Ann Scott, Amy Debra Steinhobel, Robin M. Warren, Grant Theron,

Bacterial Identification and Susceptibility Testing

Abstract Background Rapid tuberculosis (TB) drug susceptibility testing (DST) is crucial. Genotype MTBDRsl is a widely deployed World Health Organization (WHO)–endorsed assay. Programmatic performance data, including non-actionable results from smear-negative sputum, are scarce. Methods Sputa from Xpert MTB/RIF individuals (n = 951) were routinely-tested using Genotype MTBDRplus and MTBDRsl (both version 2). Phenotypic DST was the second-line drug reference standard. Discrepant results underwent Sanger sequencing. Findings 89% (849 of 951) of individuals were culture-positive (56%, 476 of 849 smear-negative). MTBDRplus had at least 1 nonactionable result (control and/or TB-detection bands absent or invalid, precluding resistance reporting) in 19% (92 of 476) of smear-negatives; for MTBDRsl, 40% (171 of 427) were nonactionable (28%, 120 of 427 false-negative TB; 17%, 51 of 427 indeterminate). In smear-negatives, MTBDRsl sensitivity for fluoroquinolones was 84% (95% confidence interval, 67%–93), 81% (54%–95%) for second-line injectable drugs, and 57% (28%–82%) for both. Specificities were 93% (89%–98%), 88% (81%–93%), and 97% (91%–99%), respectively. Twenty-three percent (172 of 746) of Xpert rifampicin-resistant specimens were MTBDRplus isoniazid-susceptible. Days-to-second-line-susceptibility reporting with the programmatic advent of MTBDRsl improved (6 [5–7] vs 37 [35–46]; P < .001). Conclusions MTBDRsl did not generate a result in 4 of 10 smear-negatives, resulting in substantial missed resistance. However, if MTBDRsl generates an actionable result, that is accurate in ruling-in resistance. Isoniazid DST remains crucial. This study provides real-world, direct, second-line susceptibility testing performance data on non-actionable results (that, if unaccounted for, cause an overestimation of test utility), accuracy, and care cascade impact.