What method is used to identify prior exposure to Mycobacterium tuberculosis?

The identification of prior exposure to Mycobacterium tuberculosis is most accurately assessed using interferon-gamma release assays (IGRAs). These tests measure the immune response to specific TB antigens by assessing the release of interferon-gamma from T-cells upon stimulation. This method is more specific for Mycobacterium tuberculosis and is not affected by prior vaccination with the Bacillus Calmette-Guérin (BCG) vaccine, which is a consideration with other testing methods.

The skin test, which involves the intradermal administration of purified protein derivative (PPD), is another commonly used method; however, it can yield false positives due to cross-reactivity with non-tuberculous mycobacteria or previous BCG vaccination. While skin testing can indicate exposure, it does not differentiate between current infection and prior exposure.

Antibody titer testing is not suitable for tuberculosis diagnosis or exposure identification. It tends to be less reliable because the immune response in infectious diseases may not always translate to measurable antibody levels, particularly with intracellular pathogens like Mycobacterium tuberculosis.

Culture methods, while they provide definitive proof of active infection by growing the bacteria from clinical specimens, do not indicate prior exposure; they are used for diagnosing active TB