Overview
Latent tuberculosis infection is a condition in which a person is infected with Mycobacterium tuberculosis-complex but does not have active tuberculosis disease. People with latent tuberculosis infection are at risk of progressing to active tuberculosis. Therefore, it is essential that individuals at high risk of progression to active tuberculosis are identified through screening.
Nearly one-third of the world’s population has latent tuberculosis infection.
Risk of progression varies based on age and comorbid conditions.
The greatest risk for progression to active disease occurs within the first 2 years of infection, during which time about 5% of individuals progress to tuberculosis disease. After the first 2 years following infection, the risk of developing active disease over an individual’s lifetime is 5–10%.
See Tuberculosis: Diagnostic Imaging and Treatment Challenges, a Critical Images slideshow, to help determine the best approach for patients with this multisystemic disease.
There is no direct test to detect the presence of latent tuberculosis infection in an individual. The screening tests for latent tuberculosis infection rely on measurements of adaptive host immune responses to the bacteria. The tuberculin skin test measures an individual’s response to a solution of Mycobacterium tuberculosis -complex antigens, known as purified protein derivative.
Until the early 2000s, the tuberculin skin test was the standard for screening for latent tuberculosis infection.
However, the test has limitations, including precise intradermal administration, the need for a follow-up visit to interpret the results, specific criteria for interpretation of the results, and the possibility of false-positive results with Bacillus Calmette-Guerin vaccination or other environmental mycobacteria.
Because of this, interferon-gamma release assays are gaining acceptance as an alternative screening test.
Because interferon-gamma release assays are performed in the laboratory, requiring one blood draw and only one patient visit to obtain results, they are significantly distinct from the traditional tuberculin skin test.