Drug resistance monitoring: combined rates may be the best indicator of programme performance

SETTING: Greater Mymensingh District, Bangladesh. OBJECTIVES: To determine changes in prevalence of drug resistance of Mycobacterium tuberculosis under DOTS. DESIGN: Drug susceptibility testing of systematic samples of M. tuberculosis isolated from all sputum smear-positive cases newly registered in sentinel centres during 1995 and 2001. Continuous, monitoring of retreatment registrations and resistance of strains from relapse and failure cases. RESULTS: Of 942 strains from the new cases in 2001, 10.8% showed resistance to any drug, 6.2% to isoniazid, 0.4% to rifampicin (all of them multidrug-resistant, MDR), 7.1% to streptomycin, and 1.0% to ethambutol. Corresponding rates for 99 strains from previously treated cases were 32%,20%, 3%,20% and 2%, respectively. Although most rates of resistance had decreased since 1995, increased streptomycin resistance was the only significant change when new and previously treated cases were considered separately. However, combined resistance for any drug, isoniazid, rifampicin and MDR had decreased significantly. CONCLUSION: As suggested by monitoring of resistance, in failure and relapse cases and by routine programme reports, drug resistance had decreased. Combined resistance demonstrated changes between periodic surveys better than its subgroups, and may be a more reliable and comprehensive indicator. However, continuous monitoring of the pool of resistant retreatment cases is a more efficient strategy.