Objectives To address whether the effect of BCG vaccination against tuberculosis (TB) infection lasts to adulthood.

Methods A cross-sectional study on the prevalence of latent TB infection (LTBI) among HIV-negative men, using QuantiFERON-TB Gold In-tube (QFT-IT), was conducted at a prison in northern Taiwan with >3000 inmates. A QFT-IT ≥0.35 IU/ml was defined as LTBI. A QFT-IT ≥0.7 IU/ml was defined as recent LTBI. The association between the number of BCG scars and LTBI stratified by age was analysed. The study procedure was approved by the institutional review board, and all participants gave written informed consent before receiving screening tests.

Results Among the 2385 participants, 25% had a QFT-IT ≥0.35 IU/ml. Increasing LTBI (14%, 32% and 50%) was observed with increased age (18–34 years, 35–54 years and ≥55 years) (p<0.001 by the Cochran–Armitage Trend Test). The number of BCG scars were found to be inversely correlated with QFT-IT results for both LTBI and recent LTBI in all three age groups (p<0.001 by Cochran–Mantel–Haenszel statistics).

Conclusions Our results suggest that BCG vaccine seems to have a protective effect in adults decades after vaccination according to the number of recent infections (QFT-IT ≥0.7 IU/ml). This finding has important implications for national policy of BCG vaccination. Further prospective cohort studies on the protective effect of BCG vaccination against TB infection in adults are warranted.