The QuantiFERON-TB-GOLD assay for tuberculosis screening in healthcare workers: a cost-comparison analysis

The aim of this study was to assess the costs of screening healthcare workers (HCWs) for tuberculosis (TB) using the novel interferon-gamma release assay QuantiFERON((R))-TB Gold In-tube (QFT) versus the tuberculin skin test (TST). We used a prospective observational study with a cost-comparison analysis. The study was conducted at a regional center for ambulatory TB treatment. The study included 100 Israeli HCWs who were referred for routine TB screening. The participants were tested with both TST and QFT. For the TST, induration of 10 mm or more was considered a positive test. For the QFT, a threshold of 0.35 IU/ml interferon-gamma above background levels was a positive test. We developed a computerized model of the present TST-only screening method versus the QFT either alone (instead of the TST) or as a confirmatory test for a positive TST. Of the 100 subjects, 34 had a positive TST result and 17 had a positive QFT result. There was poor agreement between the TST and the QFT (kappa = 0.19). Assuming adherence to treatment of 50%, costs were minimized by using the QFT to confirm a positive TST (4155). The QFT-only model was cheaper than the TST-only model (7280 vs. 8217, respectively). The QFT-only method required the fewest clinic visits (121) compared to the TST (344). Adherence to treatment in the QFT-positive group was 47% compared with 12% for the TST-positive group. Screening HCWs with the QFT test compared to the TST resulted in fewer possible cases being identified, lower costs, and increased adherence to treatment. Costs were minimized by using the QFT to confirm a positive TST. A QFT-based screening program for HCWs is feasible and should be evaluated systematically.