Strategies against multidrug-resistant tuberculosis.

The rise of multidrug-resistant tuberculosis (MDR-TB), defined as tuberculosis showing resistance to at least isoniazid and rifampicin, is a serious threat to tuberculosis control in some high prevalence countries and may have some impact on low prevalence regions as well. The World Health Organization estimates that 50 million people worldwide are infected with MDR-TB, and that, in the year 2000, 273,000 (3.1%) MDR-TB cases were among the 8.7 million new tuberculosis cases. In 1998, the highest MDR-TB rates among new cases and the highest combined (new and previously treated cases) MDR-TB rates were found in Estonia (14.1 and 18.1%), Henan province in China (10.8 and 15.1%), Latvia (9.0 and 12.0%), and Ivanovo Oblast (9.0 and 12.3%) and Tomsk Oblast (6.5 and 13.7%) in the Russian Federation. The risk factors for MDR-TB are previous treatment or relapse, originating from "hot spot" areas, a history of imprisonment, homelessness and possibly also human immunodeficiency virus. The treatment of multidrug-resistant tuberculosis is difficult due to side-effects and a treatment duration of up to 3 yrs, which is expensive and often unsuccessful. Therefore, strategies for the treatment and prevention of multidrug-resistant tuberculosis are urgently required. This requires functioning tuberculosis control programmes (directly observed treatment short course), and, in some high prevalence countries, the introduction of second-line drugs on the basis of appropriate susceptibility testing (directly observed treatment short course-Plus). Only the future will show whether this "ticking time bomb" can be defused.