Agreement between the three tests in children varied
dramatically. Widely discrepant results between QTF and TST
in children have been reported in both low and high incidence
settings.22–24 The T-SPOT.TB was positive in a significantly
higher proportion of children than the TST and the QTF. These
results suggest that the T-SPOT.TB may be a more sensitive
measure of M tuberculosis infection than the TST or QTF in
children with recent exposure, and appeared to be largely driven
by robust ESAT-6 responses. The most pronounced disagreement
between the results in children was between the TSPOT.
TB and the TST or QTF, whereas the TST and the QTF
had good agreement. Our data also suggest improved specificity
of both IGRAs compared with the TST. This could be explained
by the fact that TST responses in older individuals are
continually boosted by a variety of recurrent exposures,
including NTM25 and M tuberculosis. The clinical importance
of these observed discordances is unknown. Studies incorporating
serial follow-up measures in different populations will
support further exploration of these differences and the
predictive utility of IGRAs to identify acute and latent infection
and the subsequent risk of progressing to active tuberculosis.