Tuberculin skin testing to the IGRA positive contacts of infectious tuberculosis cases for the treatment of latent tuberculosis infection

Abstract

Background: Prospective cohort study of close contacts of smear positive tuberculosis (TB) cases. Treatment of latent TB infection (LTBI) is recommended to the contacts with positive tuberculin skin testing (TST) and interferon gamma releasing assay (IGRA) Objectives: To find out the rate of progression to active TB among IGRA positive close contacts according to the induration size of TST. Methods: Family and school contacts were followed up for about 2 years after exposure to infectious TB cases. TST until positive reaction, QuantiFERON Gold In-Tube Assay (QFT-GIT), and chest X-ray were examined at initial and 3 to 6 months after exposure. Tracing of TB cases among contacts were carried out by regular follow-up examinations and monitoring by the TB surveillance system. Results: A total of 3,088 contacts with a mean age of 15.3 ± 2.4 years old were recruited among the contacts of 117 index cases. QFT-GIT at the initial or follow up examination was positive in 530 cases (17.2%). Totally 24 close contacts (0.87%) developed active TB including 21 clinical TB. Treatment of LTBI was provided to 218 cases. Active TB among the QFT-GIT positive reactors was developed in 4 cases (2.8%) in 141 contacts with 10-14 mm induration size of TST, 14 cases (7.8%) in 180 contacts with 15-19 mm reactors, and 6 cases (10.5%) in 57 contacts with 20 mm or more reactors. No active TB case was identified among 152 contacts with 9 mm or less reactors (P=0.001). Conclusion: Treatment of LTBI may not be necessary to the contacts with positive QFT-GIT but negative TST.