2.1 Introduction
About a quarter of the world’s population has been infected with Mycobacterium tuberculosis. The vast majority of these people do not have TB disease (10). It is estimated that 7.5 million children and young adolescents aged under 15 years are newly infected with M. tuberculosis each year (11). Cumulatively, about 67 million children and young adolescents aged under 15 years are infected with M.