Extensively Drug-Resistant Tuberculosis,Taiwan

Because of these high incidences and the increasing effects of multidrug-resistant TB (MDR TB), i.e., resistant to at least both isoniazid (INH) and rifampin (RIF), the laboratory-based Taiwan Surveillance of Drug Resistance in TB (TSDRTB) program was established in 2003 (2). Surveillance demonstrated that combined drug resistance rates were 11.3% for any fi rst-line drug; and 5.3% (2004) and 4.0% (2005) for multidrug resistance. These resistance rates are higher than those reported by the third TB global drug resistance surveillance. Global surveillance reported median prevalence of combined drug resistance was 6.6% for INH, 2.2% for RIF, 1.3% for EMB, 6.1% for SM, 10.4% for any drug, and 1.7% for multidrug resistance. TB (3). Extensively drug-resistant TB (XDR TB) was initially defi ned as an MDR isolate that was resistant to at least 3 of the 6 main classes of second-line drugs: aminoglycosides, polypep-tides, fl uoroquinolones, thioamides, cycloserine, and para-aminosalicylic acid (4). In October 2006, the World Health Organization (WHO) redefi ned XDR TB as an isolate " resistant to at least INH and RIF (i.e., MDR TB) plus resistant to at least 1 of the fl uoroqui-nolones and 1 of the following 3 in-jectable drugs: capreomycin, kanamy-cin, and amikacin " (5). Clearly, XDR TB is a global threat and the demands on XDR TB surveillance systems are urgent. Because no guidelines for drug susceptibility testing of second-line drugs existed in Taiwan before 2007, clinical mycobacteriology laboratories performed drug susceptibility testing of second-line drugs using the agar proportion method by clinicians' request only. Critical concentrations of second-line drugs for drug susceptibility testing were 2 μg/mL for ofl oxacin, 6 μg/mL for kanamycin, 10 μg/mL for ethionamide, and 8 μg/ mL for para-aminosalicylate. were resistant to fl uoroquinolone, kanamycin, ethionamide, and para-aminosalicylate, respectively. Of the 116 MDR isolates tested for susceptibility to second-line drugs in 2004, 10.3% (12/116) were XDR TB; of the 99 MDR isolates tested in 2005, 10.1% (10/99) were XDR TB. With their broad spectrum anti-microbial activity, fl uoroquinolones are widely used for the treatment of bacterial respiratory infections in Tai-wan. In addition, fl uoroquinolones are the preferred oral agents for treating drug-resistant TB that is known or presumed to be sensitive to this class of drugs, or when fi rst-line agents cannot be used because of intolerance (6). In contrast to injectable agents that have a higher incidence of renal and hearing impairment after long-term use, fl uoroquinolones …