Serial T-SPOT.TB in household contacts of tuberculosis patients: a 6-year observational study in China

BACKGROUND: Screening tuberculosis (TB) contacts is a priority for TB control; however, it remains inadequate in most regions of China.OBJECTIVE: To investigate the progression of latent TB infection (LTBI) using the interferon-gamma release assay (IGRA) in contacts of active TB patients.DESIGN: This longitudinal prospective observational study included 159 household contacts aged ≥14 years without preventive treatment who were followed up for 6 years to compare their conversion and reversion rates using the T-SPOT.TB IGRA to diagnose LTBI.RESULTS: Among the 159 household contacts, LTBI positivity was 47.5%. Age was independently associated with LTBI (OR 3.6, 95%CI 1.81-7.14; P = 0.00). T-SPOT.TB conversion rates were respectively 29.4% and 18.8% at 3- and 6-year follow-up. The reversion rates were 9.4% of contacts during the 3-year follow-up period, which increased to 38.2% at the 6-year follow-up. A decreasing trend in spot-forming cells on T-SPOT.TB was observed in most patients at the 6-year follow-up.CONCLUSION: LTBI prevalence among household contacts was relatively high, particularly in elderly patients. Furthermore, serial IGRA testing was highly dynamic; however, this overall trend gradually decreased over time, even if preventive therapy was not prescribed.