Nationwide coverage of molecular drug susceptibility testing in patients with pulmonary multidrug/rifampicin-resistant tuberculosis in South Korea: a retrospective cohort study (2015-2021).

Background: We assessed the coverage of molecular drug susceptibility testing (mDST) among patients with pulmonary multidrug/rifampicin-resistant tuberculosis (MDR/RR-TB) in South Korea and identified factors influencing the lack of mDST implementation.

Methods: This retrospective study included patients with pulmonary MDR/RR-TB who initiated tuberculosis (TB) treatment between January 2015 and September 2021. Data were obtained from the K-TB-N cohort, an integrated national TB database linking three datasets. We assessed mDST coverage, temporal trends and factors associated with the lack of mDST implementation. mDST was defined as the use of the Xpert MTB/RIF assay or line probe assay (LPA) for isoniazid and rifampicin (first-line LPA).

Results: In total, 4637 patients were included in the analysis. Of the 4637 patients, 1342 (28.9%) did not undergo mDST; whereas, 3295 (71.1%) underwent mDST. Over the study period, a statistically significant annual increase in mDST coverage was observed, escalating from 49.1% in 2015 to 96.9% in 2021 (p<0.001). Throughout the study, the coverage of the Xpert MTB/RIF assay remained lower than that of LPA (22.1% vs 64.2%, p<0.001). Multivariable logistic regression analysis identified several factors independently associated with a decreased likelihood of mDST being conducted, including TB treatment initiation in secondary general hospitals, small hospitals or primary clinics, as well as in non-public-private mix (PPM) participating institutions. In addition, transfers between PPM-participating and non-participating institutions during the treatment period and sputum acid-fast bacilli smear-negative status were significantly associated with lower mDST uptake.

Conclusion: Although the increasing mDST coverage is a positive development, further efforts are needed to achieve nationwide and universal implementation, particularly for the Xpert MTB/RIF assay, in South Korea.