TABLE 2.
Performance of the Cobas TaqMan MTB test stratified by AFB smear gradea
| Smear grade | No. with PCR/culture result of: |
Performance (% [95% CI])b |
||||
|---|---|---|---|---|---|---|
| +/+ | −/− | Sensitivity | Specificity | PPV | NPV | |
| Negative | 72/159 | 6,344/6,371 | 45.3 (37.4–53.4) | 99.6 (99.4–99.7) | 72.7 (62.7–81.0) | 98.6 (98.3–98.9) |
| No AFB seen | 43/125 | 6,245/6,265 | 34.4 (26.3–43.5) | 99.7 (99.5–99.8) | 68.3 (55.2–79.1) | 98.7 (98.4–99.0) |
| Trace | 29/34 | 99/106 | 85.3 (68.2–94.4) | 93.4 (86.4–97.1) | 80.6 (63.4–91.2) | 95.2 (88.6–98.2) |
| Positive | 108/110 | 127/132 | 98.2 (92.9–99.7) | 96.2 (90.9–98.6) | 95.6 (89.5–98.4) | 98.4 (93.9–99.7) |
| 1+ | 59/61 | 79/82 | 96.7 (87.6–99.4) | 96.3 (88.9–99.1) | 95.2 (85.6–98.7) | 97.5 (90.5–99.6) |
| 2+ | 17/17 | 23/25 | 100 (77.1–100) | 92.0 (72.5–98.6) | 89.5 (65.5–98.2) | 100 (82.2–100) |
| 3+ | 13/13 | 15/15 | 100 (71.7–100) | 100 (74.7–100) | 100 (71.7–100) | 100 (74.7–100) |
| 4+ | 19/19 | 10/10 | 100 (79.1–100) | 100 (65.5–100) | 100 (79.1–100) | 100 (65.5–100) |
| Total | 180/269 | 6,471/6,503 | 66.9 (60.9–72.4) | 99.5 (99.3–99.7) | 84.9 (79.2–89.3) | 98.6 (98.3–98.9) |
a
AFB, acid-fast bacilli.
b
CI, confidence interval; PPV, positive predictive value; NPV, negative predictive value.