Ability of IGRAs for diagnosis of tuberculosis infection in adolescents, and role of non-tuberculous mycobacteria in the positivity of tuberculine skin test

Introduction: A big drawback of tuberculin skin test (TST) is the cross-reaction with bacillus Calmette-Guerin (BCG) vaccine or with non-tuberculous mycobacteria (NTM). In this way, interferon-gamma release assays (IGRAs) are more specific but few data are available for children. Aims and objectives: To assess the ability of IGRAs to detect Mycobacterium tuberculosis infection in healthy adolescents, and to know the influence of previous NTM sensitisation in discordant results as positive TST with negative IGRA. Methods: TST was performed on 2,346 students aged 12-16 from Valencia city during the 2009-10 academic year. Those with TST ≥5 mm, underwent a checkup, a chest x-ray and QuantiFERON-TB GOLD In-Tube (QFT) test. Those with negative QFT, were tested by T-SPOT.TB (TSPOT) and T cells were stimulated with Mycobacterium avium sensitin (MAS). Results: TST was ≥5 mm in 171 students (4.3%), and QFT was tested in 159. QFT was positive in 33 (21%) and it enabled to diagnose 10 individuals BCG-immunized with latent infection. QFT was negative in the 4 students with radiographic findings of previous tuberculosis (TB), and also in 14 from the 17 diagnosed with active TB. From those with negative QFT (126), TSPOT was tested in 95; it was positive in 5 (2 had been classed as vaccine reactions). Stimulation with MAS was positive in 15 (5 were not vaccinated and TSPOT was negative in all of them). Conclusions: IGRAs help to detect infection in BCG-immunized, and to rule it out in doubtful cases, avoiding unnecessary treatments. Previous NTM sensitisation may explain some positive TSTs in non-vaccinated. This work is supported by EVES and SENP grants