Table 2.
Results of MTBDRplus and MTBDRsl drug susceptibility testing using cartridge extract on clinical specimens. MTBDRplus had high indeterminate results and rifampicin-resistance false-positive rates. MTBDRsl had low indeterminate rates for both DS-TB and DR-TB specimens and performance improved when MTBDRsl was done only on specimens with CT ≤ 24.
| All Xpert TB-positive specimens | Xpert TB-positive specimens with CT ≤ 24 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Xpert rifampicin-susceptible | Xpert rifampicin-resistant | Xpert rifampicin-susceptible | Xpert rifampicin-resistant | ||||||||
| MTBDRplus (n = 56) | MTBDRsl (n = 56) | MTBDRsl (n = 29)* | MTBDRplus (n = 49) | MTBDRsl (n = 49) | MTBDRsl (n = 20)* | ||||||
| TUB-band positive (%) 47/56 (84) | TUB-band positive (%) 47/54 (96) | TUB-band positive (%) 27/29 (93) | TUB-band positive (%) 45/49 (92) | TUB-band positive (%) 49/49 (100) | TUB-band positive (%) 20/20 (100) | ||||||
| Rifampicin (%) | Fluoroquinolones (%) | Fluoroquinolones (%) | Rifampicin (%) | Fluoroquinolones (%) | Fluoroquinolones (%) | ||||||
| Susceptible | 0/47 (0) | Susceptible | 53/54 (98) | Susceptible | 14/27 (52) | Susceptible | 0/56 (0) | Susceptible | 49/49 (100) | Susceptible | 11/20 (55) |
| Resistant | 47/47 (100) | Resistant | 0/54 (0) | Resistant | 10/27 (37) | Resistant | 45/49 (92) | Resistant | 0/49 (0) | Resistant | 9/20 (45) |
| Indeterminate | 0/47 (0) | Indeterminate | 1/54 (2) | Indeterminate | 3/27 (11) | Indeterminate | 0/49 (0) | Indeterminate | 0/49 (0) | Indeterminate | 0/20 (0) |
| Isoniazid (%) | Second-line injectables %) | Second-line injectables (%) | Isoniazid (%) | Second-line injectables (%) | Second-line injectables (%) | ||||||
| Susceptible | 11/47 (23) | Susceptible | 48/54 (88) | Susceptible | 15/27 (56) | Susceptible | 11/49 (23) | Susceptible | 46/49 (94) | Susceptible | 14/20 (70) |
| Resistant | 0/47 (0) | Resistant | 3/54 (6) | Resistant | 9/27 (33) | Resistant | 0/49 (0) | Resistant | 1/49 (2) | Resistant | 6/20 (30) |
| Indeterminate | 36/47 (77) | Indeterminate | 3/54 (6) | Indeterminate | 3/27 (11) | Indeterminate | 34/49 (69) | Indeterminate | 2/49 (4) | Indeterminate | 0/20 (0) |
| TUB-band negative (%) 9/56 (16) | TUB-band negative (%) 2/56 (4) | TUB-band negative (%) 2/29 (7) | TUB-band negative (%) 4/49 (8) | TUB-band negative (%) 0/49 (0) | TUB-band negative (%) 0/20 (0) | ||||||
*For the 29 Xpert RIF-resistant specimens we were able to retrieve 20 paired culture isolates used for MTBDRsl. 18/20 matched for FQs and 17/20 for SLIDs, the 2/20 done on crude DNA had LPA results whereas the LPA on CE was TUB-band negative. 1/20 did not match for the SLID resistance. Both the TUB-band negative and discordant SLIDs result corresponded to “very low” semi-quantitation level. When defined threshold of CT ≤ 24 was applied all LPAs on CE matched LPA from culture isolates.