Abstract
Background: Limited data is available on the predictive values of Interferon-g release assays (IGRAs) and tuberculin skin test (TST) for progression to active tuberculosis (TB).
Aim: To access the positive and negative predictive values (PPV and NPV) of IGRA and TST for progression to TB disease, in recently exposed immunocompetents of positive smear sputum TB patients who did not do preventive treatment.
Methodology: Retrospective cohort of close contacts of smear-positive TB cases screened for TB from January 2007 to December 2009 – follow up until February 2011. Screening included: symptom inquiry, TST and IGRA (to confirm a positive TST ≥ 10 mm), chest radiography – negative results were re-evaluated 8-12 weeks later.
Results: 106 contacts were studied. Considering only those who did not do preventive therapy (79) - 70 tested positive for TST and 19 tested positive for IGRA (54 were already positive for TST and 16 were positive for IGRA in the first evaluation). Three contacts developed active TB: one positive for TST and IGRA at first evaluation (refused preventive treatment) and two (TST+/IGRA-) missed revaluation.
In the first evaluation, TST presented a PPV of 5.7% and a NPV of 100%; IGRA presented a PPV of 5.3% and a NPV of 96.1%. In the second evaluation, both TST and IGRA had a PPV of 0% and a NPV of 100%.
Conclusions: TST and IGRA had a better PPV for progression to TB in the initial evaluation (after index case diagnosis). A negative IGRA in the first evaluation could not exclude progression to TB.
- © 2011 ERS
