The Prevalence rate of tuberculin skin test positive by contacts group to predict the development of active tuberculosis after school outbreaks

Background: The tuberculin skin test (TST) is the standard tool to diagnose latent tuberculosis infection (ITBI) in mass screening. The aim of this study is to find an optimal cut-off point of the TST+ rate within tuberculosis ( I B) contacts to predict the active TB development among adolescents in school I B outbreaks. Methods: The Korean National Health Insurance Review and Assessment database was used to identify active TB development in relation to the initial TST (cut-off, 10 mm). The 7,475 contacts in H9 schools were divided into two groups: Incident TIJ group (43 schools) and no incident TB group (4(> schools). ITBI treatment was initiated in (>07 of the 1,7(51 TST+ contacts. The association with active TB progression was examined at different cut-off points of the TST+ rate. Results: The mean duration of follow-up was 3.9±0.9 years. Thirty-three contacts developed active TB during the 4,504 person-years among the TST+ contacts without ITBI treatment (n-1,154). The average TST+ rate for the incident TB group (n=43) and no incident TB group (n=46) were 31.0% and 15.5%, respectively. The TST+ rate per group was related with TB progression (odds ratio [OR], 1.025; 95% confidence interval [CI], 1.001-1.050; p=0.037). Based on the TST+ rate per group, active TB was best predicted at TST+ > 16% (OR, 3.11; 95% CI, 1.29-7.51; area under curve, 0.64). j Conclusion: Sixteen percent of the TST+ rate per group within the same grade students can be suggested as an optimal cut-off to predict active TB development in middle and high schools TB outbreaks.