Update on tuberculosis: TB in the early 21st century.

M ycobacterium tuberculosis infection remains a major cause of global mortality and morbidity and the resulting disease, tuberculosis (TB), caused an estimated 1.7 million deaths in 2009 [1]. However, the majority of the 2 billion people estimated to be infected with M. tuberculosis have asymptomatic infection, termed latent TB infection (LTBI) [2, 3]. Traditionally, LTBI has been defined by evidence of a cellular immune response to M. tuberculosisderived antigens, for example by the tuberculin skin test (TST) in asymptomatic individuals who have been potentially exposed to M. tuberculosis. For these individuals, the life time risk of progression from LTBI to active, symptomatic disease is only 10%; however, defects in cellular immunity can increase this risk significantly [4, 5]. Of these, the most important is HIV infection, and the ongoing HIV epidemic has helped to fuel the spread of TB globally over the past 40 yrs with 0.38 million deaths in HIV co-infected individuals in 2009 [1].