COMPARING INTERFERON-GAMMA RELEASE ASSAY WITH TUBERCULIN SKIN TEST FOR IDENTIFYING LATENT TUBERCULOSIS INFECTION BETWEEN CHILDREN < 5 YEARS AND ≥ 5 YEARS OLD

Background: The use of the interferon-gamma release assay (IGRA) for the diagnosis of latent tuberculosis infection in children under 5 years old is limited due to the low sensitivity. We compared the results of tuberculin skin test (TST) and IGRA in children under 5 years and over 5 years old who had vaccinated BCG within 4 weeks of birth in a Korean national immunization program.Methods: From December 2016 to May 2017, we included the cases who were agreed to perform an IGRA in addition to TST by parent in tuberculosis contact tracing at 5 general hospitals. TST was performed with PPD RT 23 2 TU (AJ Vaccines, Denmark) and IGRA was used with the QuantiFeron TB Gold in tube (QTF) (Qiagen, Germany).Results: A total of 80 subjects were recruited and a total of 110 tests were conducted. Forty-two (52.5%) were male, median age was 4 years of age. The percentage of intrafamilial and non-intrafamilial contact was 82.5% (66/80) and 17.5% (14/80). The result for AFB smear of index cases was positive in 33.8% (27/80), negative in 53.8% (43/80) and unknown in 12.5% (10/80). Lung cavity was seen in 27.5% (22/80) of index cases, 41.3% (33/80) had no cavity, and 31.2% (25/80) of the cases were unknown. The positive rate of TST was 43.8% (35/80), but the positive rate of QTF was only 5% (4/80). All 4 QTF positive subjects were positive for TST. The positive rate of QTF in < 2 years old, 2 to 4 years old and u2265 5 years old was 0%, 9.4%, and 3.8%. Otherwise, the positive rate of TST in < 2 years old, 2 to 4 years old and u2265 5 years old was 46.2%, 25% and 28.8%, respectively. Of the 35 TST positive cases from 110 tests, 4 (11.4%) had TST+/QTF+, and 31 (88.6%) had TST+/QTF-. Of the 75 TST negative cases, 1 (1.3%) had TST-/QTF+, and 74 (98.7%) had TST-/QTF-. The concordance of both tests was very low (Cohenu2019s kappa value = 0.1309).Conclusion: QTF positivity was much lower than TST positivity in this study. It was concluded that the use of QTF alone in children, especially younger than 5 years of age in tuberculosis contact tracing could not still acceptable due to the low concordance between TST and QTF.