Effect of anti-tuberculosis treatment on the tuberculin interferon-gamma response in tuberculin skin test (TST) positive health care workers and patients with tuberculosis

SETTING: Public hospital, Victoria, Australia. OBJECTIVE: TO evaluate the effect of multidrug treat ment and isoniazid (IN H) chemoprophylaxis on the tuberculin interferon-gamma assay (QIFN) in 19 p atients with culture-confirmed Mycobacterium tuberculosis and 119 health ca re workers (HCWs) with tuberculin skin tests (TST) greater than or equal to 15 mm. DESIGN: Patients with M. tuberculosis were treated with standard medication and tested with QIFN at diagnosis and at regular intervals over a 12-month period. All HCWs, 59 (50%) of whom were prescribed INH chemoprophylaxis, w ere tested with QIFN at baseline, 2, 4, 6 and 12 months. RESULTS: QIFN results in patients with tuberculosis were consistent and rep roducible. At the initial time point QIFN assays were positive for M. tuber culosis in 67%, and once positive, the QIFN assay remained so over the 12-m onth period. In the HCWS, initial QIFN assays were positive in 73 (61%). Du ring the 12-month study, 91 HCWs had a QIFN assay on at least two occasions . The overall reproducibility between tests was fair (kappa statistic = 0.4 5), and was little affected by administration of INH. CONCLUSION: These data suggest that although the QIFN assay is generally po sitive in patients with proven tuberculosis, it does not provide clinically useful information during the first 12 months of treatment with multidrug chemotherapy or INH chemoprophylaxis.