Multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis: epidemiology and control.

The emergence of multidrug-resistant (MDR)-TB and, more recently, of extensively drug-resistant (XDR)-TB is a real threat to achieve TB control and elimination. Over 400,000 new cases of MDR-TB occur each year and, although their number is currently unknown, XDR cases are recognized in every setting where there has been the capacity to detect them. The long-term vision for the full control of MDR-TB requires the scaling-up of culture and drug-susceptibility testing capacity, which is very limited in disease-endemic countries, and the expanded use of high-technology assays for rapid determination of resistance. MDR cases are treatable and well designed regimens, largely based on second-line anti-TB drugs, can considerably improve cure rates. However, treatment regimens need to be markedly improved through the introduction of less toxic and more powerful drugs, thus reducing duration of treatment and tolerability. This is of utmost importance for XDR-TB cases. The prevalence of MDR-TB and XDR-TB are inversely correlated with the quality of TB control and the proper use of second-line anti-TB drugs. Adherence to proper standards of care and control is imperative and a top priority of all TB control efforts. However, the risk of an uncontrollable epidemic of MDR- and XDR-TB is real considering current levels of financing and commitment to care.