Tuberculosis Drug Resistance Mutation Database

Tuberculosis (TB) remains the leading cause of death from a largely preventable and curable infectious disease, with an estimated 1.7 million deaths in 2006 [1]. Global prospects for TB control are challenged by the emergence of drug-resistant strains, especially those that are multidrug resistant (MDR) and extensively drug resistant (XDR) [2]. Soon after anti-TB drugs became available in the 1940s came reports of drug resistance among patients undergoing treatment [3]. With the advent of “short course chemotherapy” in the 1980s, the duration of treatment fell from 24 to six months, but even then full adherence to treatment regimens has been difficult to accomplish, due to the extensive length of therapy necessary to achieve cure. The prevalence of TB resistant to a single drug was continuously on the rise in several parts of the world, and eventually in the early 1990s, multiple converging factors led to an explosive emergence of MDR-TB, defined as resistance to the two most effective first-line anti-TB agents, isoniazid and rifampicin. The most recent estimates on the prevalence of anti-TB drug resistance come from surveys conducted by the World Health Organization and the International Union Against Tuberculosis and Lung Disease. These organizations investigated both new and previously treated TB cases in 93 geographical settings between 2002–2006 [4]. In these surveys, the prevalence of MDR-TB ranged from 0% to 22% among newly diagnosed cases and from 0% to 60% among previously treated cases. In addition, since 2002, 45 countries have reported cases of XDR-TB, i.e., TB that is resistant not only to isoniazid and rifampicin but also to at least one fluoroquinolone and to any of the following injectable second-line drugs: kanamycin, amikacin, or capreomycin. Of the MDR isolates tested for secondline drugs, 0%–30 % were found to be XDR [4].