Evaluation of Xpert MTB/XDR test for susceptibility testing of to first and second-line drugs in Uganda.

Background: Drug-Resistant Tuberculosis (DR-TB) is one of the key challenges toward TB control. There is an urgent need for rapid and accurate drug susceptibility tests (DST) for the most commonly used 1 and 2 line TB drugs.

Design And Methods: In a blinded, laboratory-based cross-sectional study, we set out to validate the performance of the Xpert MTB/XDR test for DST of . Sputum samples or culture isolates collected between January 2020 and December 2021 from patients with rifampicin resistance -TB and/or with higher suspicion index for isoniazid (INH) resistance and/or 2 line fluoroquinolones (FQ) and injectable agents (IAs) were tested using the Xpert MTB/XDR test from 11/September 2021 to 26/May /2022. Diagnostic accuracy and factors for laboratory uptake of Xpert MTB/XDR test were compared to MGIT960 and the Hain Genotype® MTBDR and MDRsl assays (LPA) as reference DST methods.

Results: A total of 100 stored sputum samples were included in this study. Of the samples tested using MGIT960, 65/99 (65.6%) were resistant to INH, 5/100 (5.0%) resistant to FQ and none were resistant to IAs. The sensitivity and specificity, n (%; 95%Confidence Interval, CI) of Xpert MTB/XDR test for; INH were 58 (89.2; 79.1-95.5) and 30 (88.2; 72.5-96.6), FQ; 4 (80.0; 28.3-99.4) and 95 (100; 96.2-100), respectively. The specificity for AIs was 100 (100; 96.3-100). Using LPA as a reference standard, a total of 52/98 (53.1%) were resistant to INH, 3/100 (3.0%) to FQ, and none to IA. The sensitivity and specificity, n (%; 95%CI) of Xpert MTB/XDR test compared to LPA for; INH was 50 (96.1; 86.7-99.5) and 34 (74.0; 58.8-85.7) and FQ 3 (100; 29.2-100) and 96 (99.0; 94.3-99.9) respectively. The specificity of IAs was 96 (100; 96.2-100). The factors for laboratory uptake and roll-out included; no training needed for technicians with previous Xpert-ultra experience and one day for those without, recording and reporting needs were not different from those of Xpert ultra, the error rate was 4/100 (4%), no uninterpretable results reported, test turn-around-time was 1hr/45 minutes and workflow similar to that of the Xpert-ultra test.

Conclusion: There is high sensitivity and specificity of Xpert MTB/XDR test for isoniazid, fluoroquinolones, and Injectable agents. There are acceptable Xpert MTB/XDR test attributes for test uptake and roll-out.