A prospective longitudinal study evaluating a T-cell-based assay for latent tuberculosis infection in health-care workers in a general hospital in Beijing

Abstract

Background The health-care workers (HCWs) are at high risk of acquiring infection with Mycobacterium tuberculosis. The objectives of this study were to compare the performance of the T-SPOT.TB and tuberculin skin test (TST) for latent tuberculosis infection (LTBI), evaluate diagnostic concordance and risk factors for LTBI, and observe the progression to active tuberculosis (TB) disease among HCWs in a general hospital in Beijing. Methods The prospective cohort study enrolled HCWs in a tertiary general hospital in Beijing, China, to evaluate LTBI with T-SPOT.TB and TST. The subjects were evaluated every 12 months during the 60-month follow-up. Results Of 101 participating HCWs, 96 and 101 had valid TST and T-SPOT.TB results, respectively. Twenty-nine (28.7%, 95% confidence interval (CI), 19.9%-37.5%) were defined as positive by T-SPOT.TB and 53 (55.2%, 95% CI, 45.2%-64.9%) were defined as positive by TST (using a ≥10 mm cutoff). An agreement between the two tests was poor (57.3%, κ=0.18, 95% CI, 0.01%-0.52%). In multivariate analysis, direct exposure to sputum smear-positive TB patients was a significant risk factor for a positive T-SPOT.TB (OR 5.76; 95% CI 1.38-24.00). Pooled frequency of antigen-specific IFN-γ secreting T-cells for subjects who reported direct contact with sputum smear-positive TB patients was significantly higher than that for participants without direct contact (P=0.045). One of 20 participants with positive result of T-SPOT.TB and TST developed active TB at 24-month follow-up. Conclusion T-SPOT.TB is a more accurate, targeted method of diagnosing LTBI than TST.