The global burden of disability and death due to tuberculosis (TB) is immense. In 2005 alone, an estimated 8.8 million people developed TB and almost 2 million died, including 195,000 HIV-infected individuals [1]. Although the incidence of TB is constant or falling in all regions of the world, there has been a continued increase in the total number of new TB cases in Africa, Southeast Asia and the Eastern Mediterranean region [1, 2]. The expansion of DOTS, the international TB control strategy, has resulted in a new smear-positive casedetection rate of 60% globally, approaching the 2005 WHO target of 70% case detection [1]. However, the majority of DOTS programs in high TB-burden countries have fallen short of this target [1].

More than 90% of TB patients live in lowand middle-income countries [2], where the diagnosis of TB relies primarily on identification of acid-fast bacilli on sputum smears using a conventional light microscope. In these countries, most laboratories use smears of unconcentrated sputum (direct smears) with Ziehl–Neelsen (ZN) staining. The DOTS strategy focuses on passive case finding of sputum smear-positive patients [3]. Typically, a patient who presents to a local health center or national TB program facility with a cough lasting more than 2–3 weeks