Extensively drug-resistant tuberculosis in South Korea: Risk factors and treatment outcomes among patients at a tertiary referral hospital

Background. Extensively drug-resistant (XDR) tuberculosis (TB) is a major public health threat in South Korea. Methods. We analyzed baseline epidemiological data for 250 patients enrolled in an ongoing prospective observational study of TB at a large tertiary referral hospital in South Korea. Results. Twenty-six subjects with XDR TB were identified; all were patients who had previously received TB therapy. Cumulative previous treatment duration (range, 18-34 months; odds ratio [OR], 5.6; 95% confidence interval [CI], 1.0-59), number of previously received second-line anti-TB drugs (OR, 1.3; 95% CI, 1.1-1.5), and female sex (OR, 3.2; 95% CI, 1.1-8.3) were significantly associated with XDR TB in crude analyses. After controlling for other factors in a multivariable model, cumulative previous treatment duration remained significantly associated with XDR TB (OR, 5.8; 95% CI, 1.0-61). Subjects with XDR TB were more likely to produce culture-positive sputum at 6 months, compared with patients with non-multidrug resistant TB (risk ratio, 13; 95% CI, 5.1-53). Kanamycin resistance was found to be predictive of 6-month culture positivity after adjustment for ofloxacin and streptomycin resistance (risk ratio, 3.9; 95% CI, 1.9-11). Conclusions. XDR TB was found to be associated with the cumulative duration of previous treatment with second-line TB drugs among subjects in a tertiary care TB hospital. Patients with XDR TB were more likely to not respond to therapy, and successful conversion of sputum culture results to negative was correlated with initial susceptibility to both fluoroquinolones and kanamycin but not to streptomycin.