Proportion of multidrug-resistant tuberculosis among rifampicin-resistant cases evaluated using the GeneXpert MTB/RIF assay in Western China: A retrospective observational study
Zhenzhen Zhao, Yanjun Si, Mengjiao Li, Dan Huang, Huiyu Zhong, Tangyuheng Liu, Hao Chen, Yi Zhou, Binwu YingObjective
Drug-resistant tuberculosis (TB), particularly multidrug-resistant TB (MDR-TB),tuberculosis, remains a significant public health problem in Western China. This study aimed to evaluate the prevalence of rifampicin and isoniazid resistance, including multidrug-resistant tuberculosis, and to assess the proportion of multidrug-resistant tuberculosis cases among those with rifampicin resistance as detected using GeneXpert MTB/RIF assay, with multidrug-resistant tuberculosis defined based on the MeltPro TB assay.
Methods
This retrospective observational study employed a cross-sectional diagnostic concordance design. In total, 345 patients were enrolled between December 2022 and September 2023; among these, 280 (81.16%) were newly diagnosed. Drug susceptibility profiles were determined using the MeltPro TB and GeneXpert MTB/RIF assays. Multidrug-resistant tuberculosis was defined based on the MeltPro TB assay, which served as the molecular reference rather than a definitive gold standard. Sensitivity and positive predictive value were calculated with 95% confidence intervals against MeltPro–defined multidrug-resistant tuberculosis.
Results
Among the 345 patients, 22 (6.38%) were isoniazid-monoresistant, 12 (3.48%) were rifampicin-monoresistant, and 33 (9.57%) had multidrug-resistant tuberculosis. Among the 209 samples positive on both MeltPro and GeneXpert MTB/RIF, 30 (14.35%) were rifampicin-resistant according to the GeneXpert MTB/RIF; 25 (83.33%) of these had MeltPro–defined multidrug-resistant tuberculosis. This proportion differed according to treatment history, with 11/16 (68.75%) among newly diagnosed patients versus 14/14 (100.00%) among previously treated patients. The sensitivity of GeneXpert MTB/RIF detected rifampicin resistance against MeltPro–defined multidrug-resistant tuberculosis among newly diagnosed patients was 100.00% (95% confidence interval, 71.51–100.00), and the positive predictive value was 68.75% (95% confidence interval, 44.03–87.07).
Conclusions
Only 68.75% of newly diagnosed patients with GeneXpert MTB/RIF detected rifampicin resistance had multidrug-resistant tuberculosis, indicating that rifampicin resistance is a suboptimal surrogate for multidrug-resistant tuberculosis in this population. These estimates are concordance-based rather than accuracy against a definitive reference standard, and comprehensive testing for both isoniazid and rifampicin susceptibility should be performed in clinical practice to guide treatment and mitigate transmission.