Drug-resistant tuberculosis.

The epidemic of drug-resistant tuberculosis (DR-TB) is a public health emergency that threatens to destabilise global TB control. Although TB incidence and mortality are decreasing in several parts of the world, the overall prevalence of multidrug-resistant tuberculosis (MDR-TB) is increasing in many high-burden countries, particularly in Africa.[1] World Health Organization (WHO) statistics show that almost half a million new cases of MDR-TB develop every year,[2] of which approximately 40 000 (in more than 80 countries) are thought to be extensively drug-resistant tuberculosis (XDR-TB) (Fig. 1). Limited laboratory capacity and lack of widespread drug susceptibility in resource-poor settings mean that only a fraction of that number are correctly diagnosed and started on treatment.[2] This reservoir of undiagnosed and/or untreated DR-TB is largely responsible for driving ongoing person-to-person transmission. Treatment defaulters, delays in initiating treatment, inadequate bed capacity, and poor infection control in healthcare facilities are also important contributors. In South Africa, where high transmission rates and HIV coinfection have combined to produce one of the highest incidence rates of TB in the world, the statistics are equally alarming. South Africa has the fifth highest burden of DR-TB globally, with an incidence of ~2% of new patients and ~7% of retreatment cases;[3] of these, 5 10% have XDR-TB.[4] Definitions for DR-TB are shown in Table 1.