TABLE 2.
Per-specimen smear results by different reference methods
| Reference standard test and smear method | No. of specimens (n = 579) with indicated result in reference standard test that were positive by indicated smear method |
Sensitivity [no. positive,b % (95% CIa)] | P valuec | Specificity [no. negative, % (95% CI)]d | P value | PPVe ([no. positive/total no. (%)] | NPVf ([no. negative/total no. (%)] | ||
|---|---|---|---|---|---|---|---|---|---|
|
M. tuberculosis |
Contaminated (culture) or invalid/error (Xpert) | ||||||||
| Not detected | Detected | ||||||||
| Cultureg | 402 | 169 | 8 | ||||||
| Direct | 7 | 103 | 0 | 103, 60.9 (51.4–70.5) | 0.0001 | 395, 98.3 (97.0–99.5) | 0.219 | 103/110 (93.6) | 395/461 (85.7) |
| Concentrated | 11 | 107 | 0 | 107, 63.3 (53.6–73.1) | <0.0001 | 391, 97.3 (95.7–98.9) | 0.004 | 107/118 (90.7) | 391/453 (86.3) |
| SMF | 2 | 82 | 0 | 82, 48.5 (37.4–59.6) | 400, 99.5 (98.8–100) | 82/84 (97.6) | 400/487 (82.1) | ||
| Xpert test | 429 | 150 | 0 | ||||||
| Direct | 6 | 104 | 0 | 104, 69.3 (60.4–78.2) | 0.0001 | 423, 98.6 (97.2–100) | 0.219 | 104/110 (94.5) | 423/469 (90.2) |
| Concentrated | 10 | 108 | 0 | 108, 72.0 (63.0–81.0) | <0.0001 | 419, 97.7 (96.0–99.3) | 0.008 | 108/118 (91.5) | 419/461 (90.9) |
| SMF | 2 | 82 | 0 | 82, 54.7 (43.4–65.9) | 427, 99.5 (98.9–100) | 82/84 (97.6) | 427/495 (86.3) | ||
a
Ratio estimators were used to adjust confidence intervals for specimen clustering resulting from multiple specimens per participant.
b
Sensitivity: for culture, n = 169, and for Xpert test, n = 150.
c
P values were calculated using McNemar's test. All comparisons are against SMF smear method.
d
Specificity: for culture, n = 402, and for Xpert test, n = 429.
e
PPV, positive predictive value.
f
NPV, negative predictive value.
g
Includes any culture-positive (MGIT or Lowenstein-Jensen medium) result for the same specimen.