Box 1.

Definition of Drug-Resistant Categories Based on Phenotypic DST Profiles

First-line drug resistance (FLD-R)*: Resistance to any first-line drugs (FLD) tested including INH, RIF, EMB and STM. Second-line drug resistance (SLD-R): Resistance to any second-line drugs tested including fluoroquinolones (Ofx) and second-line injectable drugs (Am, Km and Cm). Multidrug-resistance (MDR): Resistance to at least two of the most effective anti-TB drugs, INH and RIF. Non-MDR: Resistance to one or more FLD but not to INH and RIF at the same time. Quadruple drug resistance (QDR): Resistance to all four first line drugs tested including INH, RIF, EMB and STM. Fluoroquinolone resistance (FQ-R): Phenotypic resistance to any fluoroquinolone (ie Ofx in this study). Second-line injectable drug (SLID) resistance: Phenotypic resistance to at least one of three SLID including Am, Km and Cm. Extensively drug-resistant (XDR): MDR isolates simultaneously resistant to any fluoroquinolone (ie Ofx in this study) and at least to one SLID (Am, Km and Cm). Pre-extensively drug-resistant (pre-XDR): MDR isolates resistant either to any FQ (ie Ofx in this study) or one SLID (Am, Km and Cm).

Note: *Phenotypic DST is not available for pyrazinamide.

Abbreviations: Am, amikacin; Cm, capreomycin; DST, Drug susceptibility testing; EMB, ethambutol; INH, isoniazid; Km, kanamycin; Ofx, ofloxacin; R, resistance; RIF, rifampicin; STM, streptomycin.