Tuberculosis (TB) is a major global health problem and one of the most important causes of death from an infectious disease. In 2012, 8.6 million people developed TB and 1.3 million died from the disease (WHO, 2013). Despite substantial investments and progress made in the implementation of Stop TB strategy by the World Health Organization (WHO), inadequate case detection and failures to accurately classify the disease status still hamper the control of TB (Wallis et al., 2010a; McNerney et al., 2012). Most humans infected with Mycobacterium tuberculosis (MTB) remain asymptomatic, and only a small proportion develops active TB disease. Typically the bacterium establishes a latent infection and the lifetime risk of developing the disease is near 10% unless an individual becomes immunocompromised, at which time the risk increases significantly (Young et al., 2008). TB is usually a chronic, slowly progressing disease that often keeps undiagnosed in patients for many years. In adults the most common form is chronic pulmonary TB, while extrapulmonary TB is especially common in children and HIV-coinfected patients (Jain, 2011).
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The diagnosis of active TB is critical for controlling the disease. Conventional diagnostic methods of active TB include sputum smear microscopy (pulmonary TB) and M. tuberculosis isolation in bacteriological culture (currently the gold standard for definitive diagnosis of pulmonary and extrapulmonary TB). Although these methods are widely used for diagnosing TB, they suffer of specificity and sensitivity limitations (Tiwari et al., 2007; WHO, 2013), and microbiological culture takes several weeks to confirm a clinical diagnosis. Besides, both methods require highly skilled personnel and specialized laboratory infrastructure.