The authors determined the positive predictive value (PPV) for progression to tuberculosis (TB) of two interferon-c release assays (IGRAs), QuantiFERON-TB1 Gold In-tube (QFT-GIT) and T-SPOT.TB1, and the tuberculin skin test (TST) in immigrants contacts.Immigrant close contacts of sputum smear-positive TB patients were included when aged o16 yrs and their TST result was o5 mm 0 or 3 months after diagnosis of the index patient.Contacts were followed for the next 2 yrs for development of TB disease.Of 339 immigrant contacts with TST o5 mm, 324 and 299 had valid results of QFT-GIT and T-SPOT.TB1, respectively. Nine contacts developed active TB. One patient had not been tested with TST, while another patient had not been tested with QFT-GIT and T-SPOT.TB1. The PPV for progression to TB during this period was 9/28853.1% (95% CI 1.3-5.0%) for TST o10 mm, 7/ 18453.8% (95% CI 1.7-5.9%) for TST o15 mm, 5/17852.8% (95% CI 1.0-4.6%) for QFT-GIT and 6/ 18153.3% (95% CI 1.3-5.3%) for T-SPOT.TB1. Sensitivity was 100%, 88%, 63% and 75%, respectively.The predictive values of QFT-GIT, T-SPOT.TB1 and TST for progression to TB disease among immigrant close contacts were comparable.

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Preventive treatment with rifampin-pyrazinamide causes severe hepatotoxicity more often than does preventive treatment with isoniazid or curative treatment for tuberculosis.

With the IGRA as reference standard, a high proportion of persons in low-prevalence settings are treated unnecessarily for LTBI if tested with TST alone, while a small proportion eligible for preventive treatment are missed. Incremental costs of the two-step strategy seem to be balanced by the improved targeting of preventive treatment.