Figure 1

Implications of latent tuberculosis infection (LTBI) testing for progression towards tuberculosis (TB). a) After infection with Mycobacterium tuberculosis, a smaller percentage of individuals progress towards active TB, whereas the majority of individuals remain in the clinically inapparent state of latent infection with M. tuberculosis, which is defined as a state with detectable immunity in the absence of clinical symptoms. Of those, only approximately 10% of individuals, presumably those who harbour viable bacilli, progress towards TB within the next 1–2 years. b) In the same situation, the percentages of individuals with primary TB and of individuals with progression from LTBI towards TB is higher in immunocompromised patients. The largest fraction of immunocompetent and immunocompromised individuals with LTBI will never develop TB, presumably as bacilli are largely extinguished. c) When using a management strategy relying on universal screening, preventive chemotherapy is likely less effective unless combined with assessment of additional TB-related risk factors. The presence of these risk factors increases with rising TB prevalence, which necessitates management strategies adapted to the general TB prevalence in the respective region/country.