Table 3.
Performance of the Xpert MTB/XDR assay compared with the gold standard Lowenstein–Jensen proportion method for detection of resistance to isoniazid, fluoroquinolone, aminoglycoside, and ethionamide
| Method | Patient group | Drugs | L-J proportion method | Sensitivity % (95% CI) |
Specificity % (95% CI) |
PPV (95% CI) |
NPV (95% CI) |
Level of agreement (k-value) | ||
|---|---|---|---|---|---|---|---|---|---|---|
| R | S | |||||||||
| Xpert MTB/XDR assay | Overall (n = 793) | INH (n = 790) | R | 264 | 14 |
94.0 (90.5–96.4) |
97.3 (95.4–98.5) |
95.0 (91.8–96.9) |
96.7 (94.8–97.9) |
0.91 |
| S | 17 | 495 | ||||||||
| FLQ (n = 788) | R | 98 | 5 |
86.0 (78.2–91.8) |
99.3 (98.3–99.8) |
95.2 (89.1–97.9) |
97.7 (96.4–98.5) |
0.89 | ||
| S | 16 | 669 | ||||||||
| AMG (n = 760) | R | 6 | 1 |
85.7 (42.1–99.6) |
99.9 (99.3–100) |
85.7 (45.3–97.8) |
99.9 (99.2–100) |
0.86 | ||
| S | 1 | 752 | ||||||||
| ETH (n = 793) | R | 48 | 20 |
25 (19.0–31.7) |
96.7 (94.9–98.0) |
70.6 (59.4–79.8) |
80.1 (78.8–81.4) |
0.28 | ||
| S | 144 | 581 | ||||||||
| New (n = 611) | INH (n = 610) | R | 149 | 13 |
91.4 (86.0–95.2) |
97.1 (95.1–98.4) |
92.0 (87.0–95.2) |
96.9 (94.9–98.1) |
0.89 | |
| S | 14 | 434 | ||||||||
| FLQ (n = 607) | R | 53 | 5 |
79.1 (67.4–88.1) |
99.1 (97.9–99.7) |
91.4 (81.5–96.2) |
97.5 (96.0–98.4) |
0.83 | ||
| S | 14 | 535 | ||||||||
| AMG (n = 582) | R | 0 | 1 | – |
99.8 (99.1–100) |
– |
100 (99.4–100) |
– | ||
| S | 0 | 581 | ||||||||
| ETH (n = 611) | R | 29 | 12 |
19.5 (13.4–26.7) |
97.4 (95.5–98.7) |
70.7 (55.9–82.2) |
79.0 (77.6–80.3) |
0.22 | ||
| S | 120 | 450 | ||||||||
| Re-treated (n = 182) | INH (n = 180) | R | 115 | 1 |
97.5 (92.8–99.5) * |
98.4 (91.3–100) |
99.1 (94.3–99.9) |
95.3 (86.9–98.4) |
0.95 | |
| S | 3 | 61 | ||||||||
| FLQ (n = 181) | R | 45 | 0 |
95.7 (85.5–99.5) * |
100 (97.3–100) |
100 (92.1–100) |
98.5 (94.5–99.6) |
0.97 | ||
| S | 2 | 134 | ||||||||
| AMG (n = 178) | R | 6 | 0 |
85.7 (42.1–99.5) |
100 (97.9–100) |
100 (54.1–100) |
99.4 (96.5–99.9) |
0.92 | ||
| S | 1 | 171 | ||||||||
| ETH (n = 184) | R | 19 | 8 |
44.2 (29.1–60.1) * |
94.2 (89.0–97.5) |
70.4 (52.8–83.4) |
84.5 (80.7–87.7) |
0.44 | ||
| S | 24 | 131 | ||||||||
*Significant differences of proportion between the new and re-treated group of TB patients
RIF rifampicin, INH isoniazid, FLQ fluoroquinolones, AMG aminoglycoside, ETH ethionamide, R resistant, S sensitive, L-J Lowenstein–Jensen, PPV positive predictive value, NPV negative predictive value, CI confidence interval