Despite the enormous global burden of TB, approaches to TB diagnosis still rely on traditional methods that have major limitations. The disproportionate amount of smear -negative disease in sub-Saharan Africa , which shoulders two -thirds of the global burden of HIV/AIDS, has greatly complicated TB case detection and disease control.

Multidrug -resistant (MDR) TB, defined as resistance to both isoniazid and rifampicin, two of the most important “first- line” anti-TB drugs, is a rapidly growing problem, especially in Eastern Europe and countries of the former Soviet Union. Even more alarming is the recently documented phenomenon of XDR (or extensive ly drug- resistant) TB, defined not only as resistance to isoniazid and rifampicin but also to one second line injectable agent and a fluoroquinolone antibiotic. XDR TB is often not curable with available drugs