First insight into latent tuberculosis infection among household contacts of tuberculosis patients in Duhok, Iraqi Kurdistan: using tuberculin skin test and QuantiFERON-TB Gold Plus test

BACKGROUND: The objectives were to estimate the prevalence of latent tuberculosis infection (LTBI) among household contacts (HHCs) with active TB patients, and to identify their risk factors. METHODS: A prospective, cross sectional study was conducted from May to October 2018. All HHCs with active TB cases were included. The subjects underwent two tests: Quantiferon TB-Gold plus assay (QFT-Plus) and tuberculin skin test (TST). Data were analyzed using the Statistical Package for Social Sciences 25. RESULTS: Among 521 HHCs, 101 (24.05%) revealed positive TST and 80 (19.85%) positive QFT-Plus. The significant risk factors associated with positive TST individuals were ≥ 15 years, immunosuppressive therapy, and pulmonary TB (PTB) patients; whereas, those with QFT-Plus positive were ≥ 45 years, alcohol consumption, and immunosuppressive therapy. The concordance rate among 309 individuals who performed both tests was 0.88 %; the kappa value showed good agreement (k = 0.679) and significant correlation (P < 0.001). CONCLUSIONS: The overall rate of LTBI was intermediate. Screening of LTBI should be routine among HHCs, regardless of the site of the disease. Age ≥ 15 years, alcoholics, immunosuppressive therapy, and PTB were potential risk factors. There was a good concordance between TST and QFT-Plus. A QFT-Plus can overcome the limitation of a BCG vaccinated individual, especially in early life.