Methods: Data collected from index patients included age, sex, occupation, disease status, results of AFB smear / culture and chest x-ray. Data collected from contacts included age, sex, results of serial tuberculin skin test (TST) and chest x-ray. Congregate settings included childcare centers, kindergartens, elementary and secondary schools, and age groups were stratified as follows: 0-4 years, 5-12 years and 13-18 years. TSTs were considered positive if induration ≥10 mm on the first test (TST1) or demonstrated an increase ≥6 mm over the induration of TST1 on repeat testing after 8 weeks (TST2).
Results: Of the 197,801 subjects with data collected, 173,998 were eligible and included in our analysis. TST1 results were available for 159,346 (91.6%) and when results were positive, induration was 10-14 mm in 7.6% and ≥15 mm in 1.5%. TST2 results were available for 119,797 (82.7%) of the 144,904 with negative TST1, and conversion rate was 9.0%. Altogether considering TST1 and TST2, 17.3% contacts had latent TB infections. Positive rates of TST significantly decreased with age: 20.3% in 0-4 years, 18.8% in 5-12 years, 17.1% in 13-18 years.
Conclusion: In this 3-year school-setting contact investigation, 17.3% contacts were diagnosed with latent TB infection, as demonstrated by TST reactions. Positive rates of TST significantly but mildly decreased with age.
J. H. Hwang, None
S. Lee, None
K. H. Lee, None
M. Park, None