Background: We analyzed the prevalence of anti-tuberculosis drug resistance in Mycobacterium tuberculosis isolates from respiratory specimens of patients with newly diagnosed and previously treated tuberculosis.

Methods: From February 2010 to July 2010, a total of 542 M. tuberculosis clinical isolates were collected from pulmonary tuberculosis patients in six university hospitals distributed throughout Korea. We analyzed the results of anti-tuberculosis drug resistance tests according to treatment history and geographic location.

Results: Among the 542 isolates, 473 (87.3%) were from newly diagnosed cases and 69 (12.7%) were from previously treated cases. The rates of multi-drug resistance (MDR), fluoroquinolone (ofloxacin, levofloxacin, and moxifloxacin) resistance, and extensive drug resistance (XDR) were 3.8%, 1.1-1.5%, and 0%, respectively, in new cases, and 21.7%, 13.0-17.4%, and 4.3%, respectively, in previously treated cases. In the previously treated cases, the proportions of XDR-TB in MDR-TB were 20% (3/15). The resistance rates were variable according to geographic location.

Conclusion: As the anti-tuberculosis drug resistance rates are much higher in newly diagnosed cases than in previously treated patients, efforts should be made to ensure that tuberculosis treatment is successful. In addition, before the selection of an anti-tuberculosis drug treatment for previously treated patients, the susceptibility test results, including to fluoroquinolone, should be verified. (Ann Clin Microbiol 2013;16:1-7)