Tuberculin skin testing in BCG-vaccinated populations of adults and children at high risk for tuberculosis in Taiwan.

SETTING

Various populations at high risk for tuberculosis (TB) infection and with high bacille Calmette-Guérin (BCG) vaccination coverage in eastern Taiwan.

OBJECTIVE

To investigate the usefulness of the tuberculin skin test (TST) to diagnose TB in BCG-vaccinated populations.

DESIGN

Cross-sectional survey.

RESULTS

TST reaction size was recorded for 444 individuals ranging in age from 8 months to 99 years, of whom 94.3% had scars to suggest previous BCG vaccination. The TST-positive (> or =10 mm) rate was increased in all comparisons of higher to lower TB risk, including household contacts (relative risk [RR] 3.52, P < 0.0001) and intermediate risk residents (RR 2.30, P = 0.030) compared to a lower risk control group. Advancing age was generally associated with increases in the TST-positive rate. Gender or the number of BCG vaccinations had no relation to the TST-positive rate.

CONCLUSIONS

The results of this survey suggest that in eastern Taiwan a positive TST represents either active or latent TB infection rather than past BCG vaccination. Therefore, high BCG vaccination coverage in this region does not appear to limit the usefulness of the TST as a tool for diagnosing TB.