Primary drug resistance in extra-pulmonary tuberculosis: a hospital-based prospective study from Pakistan

SETTING: Tertiary level specialised tuberculosis (TB) hospital. OBJECTIVE : To determine the prevalence of antimicrobial resistance in new extra-pulmonary tuberculosis (EPTB) cases. DESIGN: Prospective cross-sectional study. Presumptive EPTB patients with enlarged lymph nodes or pleural effusion having no history of TB treatment were enrolled. Specimens were tested for smear, Xpert (R) MTB/RIF and culture. Indirect drug susceptibility testing (DST) was performed using MGIT 960 and line-probe assays (LPA). RESULTS : Among 671 cases, 255 were bacteriologically confirmed and 185 DSTs were performed. Multidrug resistance (MDR-TB) was reported in 2.2% (95% CI 0.6-5.4), any resistance to rifampicin (RMP) in 2.7% (95% CI 0.9-6.2), isoniazid (INH) in 7.6% (95% CI 4.1-12.4), ethambutol in 1.1% (95% CI 0.1-3.9), pyrazinamide in 2.2% (95% CI 0.9-5.5) and fluoroquinolones (FQ) in 6.0% (95% CI 3.0-10.4). The sensitivity and specificity of LPA-DST was 100% and >98.8% respectively for RMP, INH and FQ. Among 82 cases with RMP of the results available for all three methods used, five were reported to be resistant on Xpert but all five were susceptible on MGIT 960 and four on MTBDRplus. CONCLUSION: Prevalence of RMP resistance in new EPTB cases is 2.7% (95% CI 0.9-6.2). Caution is warranted for RMP resistance detected using Xpert in EPTB samples with a very low bacterial load.