DNA from used Xpert MTB/RIF Ultra cartridges obtained using the CREDO extraction device reduces drug-resistant tuberculosis care cascade gaps in a routine laboratory
1
TB, DR-TB & CDC Directorate, Department of Health, Bloemfontein, South Africa
2
Medical Microbiology, Universitas Academic Laboratory, National Health Laboratory Service,, Bloemfontein, South Africa
3
Medical Microbiology, School of Pathology, Faculty of Health Sciences, University of the Free State, Bloemfontein, South Africa
4
Department of Biomedical Sciences, Division of Molecular Biology and Human Genetics, University of Stellenbosch, DSI-NRF Centre of Excellence for Biomedical Tuberculosis Research and SA/MRC Centre for Tuberculosis Research, Cape Town, South Africa
Popul. Med. 2026;8(Supplement Supplement 1):A651
ABSTRACT
BACKGROUND:
Tuberculosis (TB) second-line drug susceptibility testing (DST) typically requires a second specimen, which is not always available. We evaluated a device to retrieve cartridge extract (CE) containing DNA from used Xpert MTB/RIF Ultra (Ultra) TB-positive cartridges for second-line DST (MTBDRsl assay) in a routine high-volume laboratory.
METHODS:
We collected 103 rifampicin-resistant TB–positive Ultra cartridges from programmatic laboratories in Free State, South Africa (03/08/2022–09/09/2023). Cartridge extracts (CEs) were obtained using the CREDO device (n=70) or a needle-based approach (n=33); CEs with CTmin >25 were excluded (n=23). MTBDRsl was performed on all CEs, with MGIT960 culture from paired or recent (<3 months) sputum (when available) and routinely available diagnostic results as reference for diagnostic yield and for comparing time-to-treatment. The proportion of cases lacking routine DST but yielding successful CE MTBDRsl results was also assessed.
RESULTS:
Both CREDO and needle methods yielded sufficient DNA with no significant difference in success rates (36/50; 72% vs 26/30; 87%; p = 0.128). 80/103 (78%) met threshold and were tested with MTBDRsl, of which 72/80 (90%) were successful for TB detection, and strongly associated with high Ultra semi-quantitation (high/medium >90% vs low 55%; p < 0.0001). DST showed that most successful CEs were susceptible: 55/63 (87%) for fluoroquinolones (FQs) and 57/59 (97%) for second-line injectable drugs (SLIDs). Where no routine DST was available, the CE approach detected additional DST for 26/103 (26%) FQs and 5/26 (19%) SLIDs, detecting five previously unrecognised resistances (one in Group 2, four in Group 3).
CONCLUSIONS:
The CE method showed concordance with routinely generated results, and in instances where no WHO-recommended genotypic DST for second-line drugs were available, we increased the proportion of people who received a DST by ~14%, demonstrating that repurposing discarded Ultra cartridges for MTBDRsl is a feasible way to allow DST when follow-up specimens are unavailable.
Tuberculosis (TB) second-line drug susceptibility testing (DST) typically requires a second specimen, which is not always available. We evaluated a device to retrieve cartridge extract (CE) containing DNA from used Xpert MTB/RIF Ultra (Ultra) TB-positive cartridges for second-line DST (MTBDRsl assay) in a routine high-volume laboratory.
METHODS:
We collected 103 rifampicin-resistant TB–positive Ultra cartridges from programmatic laboratories in Free State, South Africa (03/08/2022–09/09/2023). Cartridge extracts (CEs) were obtained using the CREDO device (n=70) or a needle-based approach (n=33); CEs with CTmin >25 were excluded (n=23). MTBDRsl was performed on all CEs, with MGIT960 culture from paired or recent (<3 months) sputum (when available) and routinely available diagnostic results as reference for diagnostic yield and for comparing time-to-treatment. The proportion of cases lacking routine DST but yielding successful CE MTBDRsl results was also assessed.
RESULTS:
Both CREDO and needle methods yielded sufficient DNA with no significant difference in success rates (36/50; 72% vs 26/30; 87%; p = 0.128). 80/103 (78%) met threshold and were tested with MTBDRsl, of which 72/80 (90%) were successful for TB detection, and strongly associated with high Ultra semi-quantitation (high/medium >90% vs low 55%; p < 0.0001). DST showed that most successful CEs were susceptible: 55/63 (87%) for fluoroquinolones (FQs) and 57/59 (97%) for second-line injectable drugs (SLIDs). Where no routine DST was available, the CE approach detected additional DST for 26/103 (26%) FQs and 5/26 (19%) SLIDs, detecting five previously unrecognised resistances (one in Group 2, four in Group 3).
CONCLUSIONS:
The CE method showed concordance with routinely generated results, and in instances where no WHO-recommended genotypic DST for second-line drugs were available, we increased the proportion of people who received a DST by ~14%, demonstrating that repurposing discarded Ultra cartridges for MTBDRsl is a feasible way to allow DST when follow-up specimens are unavailable.
| eISSN: | 2654-1459 |
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