Differences in rpoB, katG and inhA mutations between new and previously treated tuberculosis cases using the GenoType MTBDRplus assay

Drug resistance in new cases reflects primary transmission of resistant strains, while drug resistance in previously treated patients is more likely to reflect acquired resistance during previous tuberculosis (TB) treatment. In this study from a rural hospital in South India, we compared molecular differences between new and previously treated TB patients who had isoniazid or rifampicin resistance-conferring mutations using the GenoType MTBDRplus assay. Out of 2112 TB patients, 245 (11.6%) had rpoB mutations and 338 (16%) had isoniazid resistance-conferring mutations. Among patients with rpoB mutations, the proportion of new and previously treated cases with no isoniazid resistance-conferring mutations was 41.2% and 26% (P-value = 0.02; risk ratio [RR] 1.58, 95% confidence interval [CI] 1.09–2.31; risk difference [RD] 15.2%, 95% CI 18.2–28.6), respectively. Among patients with isoniazid resistance-conferring mutations, the proportion of new and previously treated cases with no rpoB mutations was 71.8% and 33.2% (P-value