Extensively drug-resistant Mycobacterium tuberculosis during a trend of decreasing drug resistance from 2000 through 2006 at a medical center in Taiwan

Background. Drug resistance rates are one of the most important aspects in the national tuberculosis (TB) control program, and drug-resistant TB, especially extensively drug-resistant (XDR) TB, is not well understood in Taiwan. The objectives of this study were to investigate the prevalence of drug resistance from 2000 through 2006 and to identify XDR TB isolates to elucidate the clinical characteristics of patients with XDR TB at National Taiwan University Hospital. Methods. The prevalence of drug resistance among clinical, nonduplicate Mycobacterium tuberculosis isolates was analyzed. Testing of susceptibility to antituberculosis agents, including isoniazid, rifampicin, ethambutol, streptomycin, rifabutin, ofloxacin, ethinamide, and para-aminosalicylic acid, was performed using the proportional method. Minimum inhibitory concentrations of amikacin, capreomycin, isepamycin, linezolid, cycloserine, ciprofloxacin, levofloxacin, moxifloxacin, and gemifloxacin were determined for 40 available multidrug-resistant M. tuberculosis isolates. Results. Significant decreasing trends in rates of resistance to isoniazid, ethambutol, and at least 1 of the 3 first-line agents were observed among 2625 M. tuberculosis isolates from 2000 through 2006. Among these 2625 isolates, 150 (5.7%) were multidrug resistant, and 10 M. tuberculosis isolates (0.4%) fulfilled the definition of XDR M. tuberculosis. Nine (90%) of 10 patients with XDR TB had a previous history of TB and received anti-TB treatment before acquisition of XDR TB. Conclusions. The remaining high prevalence of multidrug-resistant TB and the presence of XDR TB during a trend of decreasing drug resistance are alarming. Continuous surveillance of clinical isolates of M. tuberculosis is needed to identify XDR TB, especially in patients who have a history of TB and have received prior anti-TB treatment.