Fitness costs of drug resistance mutations in multidrug-resistant mycobacterium tuberculosis: A household-based case-control study

Background The projected long-term prevalence of multidrug-resistant (MDR) tuberculosis depends upon the relative fitness of MDR Mycobacterium tuberculosis strains, compared with non-MDR strains. While many experimental models have tested the in vitro or in vivo fitness costs of various drug resistance mutations, fewer epidemiologic studies have attempted to validate these experimental findings. Methods We performed a case-control study comparing drug resistance-associated mutations from MDR M. tuberculosis strains causing multiple cases in a household to matched MDR strains without evidence of secondary household cases. Results Eighty-eight multiple-case and 88 single-case household MDR strains were analyzed for 10 specific drug resistance-associated polymorphisms previously associated with fitness effects. We found that the isoniazid-resistant katG Ser315Thr mutation occurred more than twice as frequently in multiple-case households than in single-case households (odds ratio [OR], 2.39; 95% confidence interval [CI], 1.21-4.70), corroborating previous experimental findings. However, strains carrying both the katG Ser315Thr mutation and the rpsL Lys43Arg mutation were less likely to be found in multiple-case households (OR, 0.09; 95% CI,. 01-.73), suggesting a negative epistatic interaction which contrasts previous findings. Conclusions The case-control design presents a useful approach for assessing in vivo fitness effects of drug resistance mutations.