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

OBJECTIVE

To investigate the usefulness of confirmatory QuantiFERON(®) (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.