Latent tuberculosis (LTB) is defined as a state of persistent immune response to
Mycobacterium tuberculosis antigens as a result of previously acquired infection and without
evidence of clinically manifested active tuberculosis (TB).1 About a quarter of the world’s
population has latent TB (LTB).2 By traditionally accepted estimates, approximately 5–10% of
people with LTB will develop active TB in their lifetime, one half within the first 2 years
following infection. The period of highest risk is within the first year following an individual’s
infection.