Abstract:
Background: The new Xpert MTB/RIF Ultra was introduced to overcome imperfect sensitivity
of first generation Xpert MTB/RIF in detection of tuberculosis (TB) and rifampicin-resistance.
Given the rapid changes in the TB diagnostic arena, the added value of Xpert MTB/RIF Ultra for
detection of RIF-resistant M. tuberculosis compared to VER 2.0 LPA and phenotypic drug
susceptibility test (DST) is not well investigated.
Objectives: To compare diagnostic performance of Xpert MTB/RIF Ultra and MTBDRplus VER
2.0 line probe assay in detection of rifampicin-resistant M. tuberculosis in Jimma University
Medical Center, Southwest Ethiopia.
Methods: A Hospital based cross-sectional study was conducted from June 2020 to October
2021 in Jimma, Southwest Ethiopia. A total of 275 pulmonary TB suspected patients were
selected consecutively. Each study participants provided two cups of sputum samples. The first
cup of sputum was subjected for Xpert MTB/RIF Ultra and the second sputum was processed for
culture. Culture positive isolates were subjected for MGIT-DST and LPA. Sensitivity and
specificity were determined to assess the performance characteristics of the Ultra and LPA.
Results: Of 275 paired-sputum samples tested, altogether 57 culture and Ultra positive samples
were included. By MGIT-DST, 21 isolates were rifampicin-resistant and 36 were rifampicin sensitive. There was one discrepant result, which was rifampicin-sensitive by Ultra but
rifampicin-resistant by MGIT-DST. Against MGIT-DST as the gold standard, Ultra had a
sensitivity and specificity of 95.5% and 100% respectively and showed excellent agreement with
MGIT-DST (Kappa=0.96 (95%CI =88.8-99.8)). LPA correctly detected all rifampicin-resistant
cases detected by MGIT-DST with 100% sensitivity and 100% specificity. We also found 96%
overall agreement of two molecular methods (Ultra and LPA) for the detection of rifampicin resistance.
Conclusion: Ultra has similar diagnostic performance with that of LPA for the detection of
rifampicin-resistance. Considering its shorter turn-around time, relatively easier to perform and
minimum biosafety requirement, the new Xpert MTB/RIF Ultra can be used for the detection of
rifampicin-resistant and to screen for MDR-TB in Ethiopia.
