Role of confirmatory interferon-gamma release assays in school outbreaks of tuberculosis in South Korea

Abstract

OBJECTIVE: To investigate the usefulness of confirmatory QuantiFERON (R) (QFT) testing among tuberculin skin test (TST) positive contacts to diagnose latent tuberculous infection (LTBI) in tuberculosis (TB) outbreaks among adolescents. DESIGN: We used the Korean national claims database to identify the development of active TB disease in relation to initial TST (cut-off 10 mm induration) and subsequent QFT results. RESULTS: A total of 7475 contacts in 89 schools were divided into four groups: TST (n=5714), TST+/QFT+ (n = 534), TST+/QFT (n = 697) and TST+ only (n = 530). The mean duration of follow-up was 3.9 +/- 0.9 years. For contacts with no LTBI treatment (n = 6868), TB incidence rates per 1000 person-years (py) and the adjusted hazard ratio (HR) compared with TST-individuals were as follows: TST+/QFT+, 66.2/1000 py (HR 35.59, 95%CI 14.03-90.31, P < 0.001); TST+ only, 10.1/1000 py (HR 5.16, 95%CI 2.91-9.17, P < 0.001); TST+/QFT, 4.0/1000 py (HR 2.05, 95%CI 1.05-4.01, P= 0.035); and TST - 2.0/1000 py. The TB progression rate was significantly higher in TST+/QFT+ than in TST+/QFT individuals (HR 16.82, 95 CI 5.84-48.46, P < 0.001). CONCLUSION: A confirmatory QFT for TST+ contacts could reduce the number of candidates for LTBI treatment after school TB outbreaks. KEY WORDS: latent tuberculous