Latent infection with Mycobacterium tuberculosis

Mycobacterium tuberculosis has two distinct stages in a human host: latent infection, where the bacteria do not actively reproduce and the host remains asymptomatic, and tuberculosis (TB) disease, where the bacteria actively reproduce causing the host to become ill. Latent infection may remain clinically silent and unrecognized for life or it may be activated into clinical disease after a prolonged period of time. The prevalence of latent infection with M. tuberculosis usually increases with age, is higher among males than females, and varies with socioeconomic determinants. Tuberculin skin test and Interferon-γ Release Assays (IGRAs) are used to identify persons who have been latently infected by M. tuberculosis. While IGRAs have a high specificity among both BCG-vaccinated and unvaccinated populations as compared with the tuberculin skin test, positive predictive value for the risk of progression to TB among those who had positive test results of IGRA remains relatively low. Potential strategies to improve our ability to address latent infection with M. tuberculosis include reducing risk of transmission (intensified case finding and effective case management, infection control, and preexposure vaccine), reducing risk of progression (risk factor management, preventive chemotherapy, and postexposure vaccine), and developing new diagnostics with better predictive power.