Table 2. Resistance detection results by Xpert MTB/RIF Ultra on Omni versus GeneXpert devices for rifampicin-resistant specimens.
| Result of test | Omni | ||||
|---|---|---|---|---|---|
| RIF-R | RIF-S | Indeterminate | Total (%) | ||
| GeneXpert | RIF-R | 145 (92.9%) | 0 (0.0%) | 2 (1.3%) | 147 (93.1%) |
| RIF-S | 1a (0.6%) | 1b (0.6%) | 1 (0.6%) | 3 (1.9%) | |
| Indeterminate | 2 (1.3%) | 2 (1.3%) | 2 (1.3%) | 6 (3.8%) | |
| Total | 148 (94.9%) | 3 (1.9%) | 5 (3.2%) | 156 (100%) | |
RIF-R: rifampicin resistance detected, RIF-S: rifampicin resistance not detected. All percentages are based on the total number of RIF resistant cases for which a RIF resistance call was made by both devices (n = 156).
a This discordant specimen with an rpoB H445Y mutation (a known, high-confidence resistance-conferring mutation) was characterized in the FIND specimen bank as phenotypically RIF-resistant, smear-negative, culture-positive and ‘very low’ positive on MTB Ultra testing on both GeneXpert and Omni.
b This discordant specimen with rpoB D435G & I491F mutations (known resistance-conferring mutations) was characterized in the FIND specimen bank as phenotypically RIF-resistant, smear-positive (scanty), culture-positive and ‘low’ positive on MTB Ultra testing on both GeneXpert and Omni.