ESAT-6, a RD-1-encoded M. tuberculosis-specific antigen, is an accurate marker of M. tuberculosis infection; it discriminates against BCG because the RD-1 region is deleted from such strains [ 20- 24, 24, 35].
Thus T-cell responses to these antigens are not confounded by prior BCG vaccination and are a more specific immune marker of M. tuberculosis infection than TST.
A positive TST response is a marker of TB exposure and also increases the likelihood of occurrence of TB in a child with suspected pulmonary tuberculosis.
For example, a volatile organic compound called methyl nicotine produced by Mycobacterium tuberculosis bacteria can be used as a noninvasive and rapid diagnostic marker for detection of Tuberculosis (TB) diseases [ 12].
A number of studies have pointed out that IGRAs may also have a higher specificity than TST for the diagnosis of LTBI in low TB incidence settings and correlate better with surrogate markers of M. tuberculosis exposure [ 27, 28].
Newer testing modalities with interferon-gamma release assays (QuantiFERON-TB Gold or In-Tube and T-SPOT TB) have improved the specificity of the diagnosis as they are more specific markers of M. tuberculosis infection and previous exposure and are not influenced by BCG vaccination or exposure to atypical mycobacteria.
Odds ratios (ORs) were used to estimate the likelihood of infection in HHCs compared to that of individuals from the SP, using TST and IFNγ response to CFP-10 as surrogate markers of M. tuberculosis infection.
Identifying genetic markers of M. tuberculosis virulence would enable additional attention to be focused on patients infected with strains manifesting such markers and who are therefore at the greatest risk for poor outcomes.
As childhood TB results from recent infection and subsequent disease development, children serve as a sentinel marker of ongoing M. tuberculosis transmission and failing TB control within a community [ 5].
