Table 5. Performance characteristics of the Xpert MTB/RIF test stratified by participant TB treatment status, using MGIT culture as the reference standarda.
| No current or prior TB treatment | Current TB treatment | Prior but not current TB treatment | ||
| N = 5764b | N = 58 | N = 797 | ||
| Xpert sensitivity | N/N | 96/155 | 4/4 | 17/28 |
| % (95% CI) | 61.9 (53.8, 69.6) | 100 (39.8, 100.0) | 60.7 (40.6, 78.5) | |
| Xpert specificity | N/N | 5599/5609 | 46/54 | 760/769 |
| % (95% CI) | 99.8 (99.7, 99.9) | 85.2 (72.9, 93.4) | 98.8 (97.8, 99.5) | |
| Xpert PPV | N/N | 96/106 | 4/12 | 17/26 |
| % (95% CI) | 90.6 (83.3, 95.4) | 33.3 (9.9, 65.1) | 65.4 (44.3, 82.8) | |
| Xpert NPV | N/N | 5599/5658 | 46/46 | 760/771 |
| % (95% CI) | 99.0 (98.7, 99.2) | 100.0 (92.3, 100.0) | 98.6 (97.5, 99.3) | |
| Agreement between Xpert and MGIT | N/N | 5695/5764 | 50/58 | 777/797 |
| % (95% CI) | 98.8 (98.5, 99.1) | 86.2 (74.6, 93.9) | 97.5 (96.2, 98.5) |
Abbreviations: CI, confidence interval; MGIT, Mycobacteria Growth Indicator Tube; PPV, positive predictive value; NPV, negative predictive value.
a
Excluded from the analyses were 249 specimens that were contaminated in MGIT culture, 23 specimens that had a final result of failed on Xpert MTB/RIF testing, and 2 specimens from participants for whom data on TB treatment status were missing.
b
four participants who reported not being on current TB treatment but did not know if they had ever been on TB treatment were coded as “no current or prior TB treatment”.