Table 2. Performance of the Xpert test for the detection of MTBC, compared to smear and culture results.
| Culture results, no. | Performance %, (95% CI) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| MTBC | NTM | Total | Sensitivity | Specificity | PPV | NPV | |||
| Positive | Negative | ||||||||
| Xpert results, n = 2726* | |||||||||
| MTBC detected | 704 | 211 | 43 | 958 | 73.6 | 85.7 | 73.5 | 85.8 | |
| MTBC not detected | 252 | 1319 | 197 | 1768 | (70.7–76.4) | (83.9–87.3) | (71.1–75.8) | (84.4–87.0) | |
| Total | 956 | 1530 | 240 | 2726 | |||||
| AFB smear results, n = 2667# | |||||||||
| Smear-positive | 584 | 360 | 151 | 1095 | 63.0 | 70.6 | 55.3 | 78.2 | |
| Smear-negative | 343 | 1154 | 75 | 1572 | (59.8–66.1) | (68.4–72.8) | (51.1–55.5) | (76.6–79.7) | |
| Total | 927 | 1514 | 226 | 2667 | |||||
| Xpert results stratified by AFB smear results | |||||||||
| Smear-positive | Xpert (+) | 552 | 150 | 35 | 737 | 94.5 | 63.8 | 74.9 | 91.1 |
| Xpert (-) | 32 | 210 | 116 | 358 | (92.4–96.2) | (59.5–68.0) | (72.6–77.0) | (87.9–93.5) | |
| Total | 584 | 360 | 151 | 1095 | |||||
| Smear-negative | Xpert (+) | 132 | 52 | 6 | 190 | 38.7 | 95.5 | 69.5 | 84.8 |
| Xpert (-) | 209 | 1100 | 69 | 1378 | (33.5–44.1) | (93.9–96.4) | (63.1–75.2) | (83.7–85.9) | |
| Total | 341 | 1152 | 75 | 1568 | |||||
Abbreviations: MTBC, Mycobacterium tuberculosis complex; NTM, nontuberculous mycobacteria
* Of 2957 tested specimens, 231 were excluded from the analysis due to missing culture results and MTBC-indeterminate results.
# Sixty-three cases were excluded from the analysis due to missing smear results.