Table 3.
Sensitivity and Specificity of the MTB/RIF Test for the Detection of Rifampin and Multidrug Resistance, as Compared with Phenotypic Drug-Susceptibility Testing Alone and in Combination with Sequencing of Discrepant Cases, According to Site.*
| Site and Total | Phenotypic Drug-Susceptibility Testing† | Phenotypic Drug-Susceptibility Testing and Discrepant Resolution by Sequencing† | ||
|---|---|---|---|---|
| Sensitivity for Rifampin Resistance | Specificity for Rifampin Resistance | Sensitivity for Rifampin Resistance | Specificity for Rifampin Resistance | |
| Lima, Peru — no./total no. (%) | 16/16 (100.0) | 190/193 (98.4) | 19/19 (100.0) | 190/190 (100.0) |
| Baku, Azerbaijan — no./total no. (%) | 47/49 (95.9) | 90/94 (95.7) | 51/52 (98.1) | 90/90 (100.0) |
| Cape Town, South Africa — no./total no. (%) | 15/16 (93.8) | 126/126 (100.0) | 15/15 (100.0) | 126/126 (100.0) |
| Durban, South Africa — no./total no. (%) | 3/3 (100.0) | 38/38 (100.0) | 3/3 (100.0) | 38/38 (100.0) |
| Mumbai, India — no./total no. (%) | 119/121 (98.3) | 61/64 (95.3) | 121/122 (99.2) | 62/62 (100.0) |
| Total for rifampin resistance | ||||
| Correct — no./total no. (%) | 200/205 (97.6) | 505/515 (98.1) | 209/211 (99.1) | 506/506 (100.0) |
| 95% CI — % | 94.4–99.0 | 96.5–98.9 | 96.6–99.7 | 99.2–100.0 |
| Total for multidrug resistance | ||||
| Correct — no. /total no. (%) | 195/200 (97.5) | 197/199 (99.0) | ||
| 95% CI — % | 94.3–98.9 | 96.4–99.7 | ||
Multidrug resistance is defined as resistance to both rifampin and isoniazid. Of 723 culture-positive samples, 720 were analyzed for rifampin resistance because results on the MTB/RIF test were indeterminate in 3 cases. During blinded sequencing of 15 discrepant samples, rpoB mutations were identified in 9 samples that were rifampin-sensitive on phenotypic drug-susceptibility testing. A wild-type allele was identified in 1 sample, which had been reported as resistant on phenotypic drug-susceptibility testing. Mixed infections were identified in 3 samples and were excluded from the analysis after discrepant resolution. In 2 samples, sequencing confirmed the phenotypic result: rpoB mutation 516 GTC was detected in 1, and 531 TTG in the other.
This is the reference standard for the comparison with the MTB/RIF test.