Prevalence of Latent Tuberculosis Infection (LTBI) among House Hold Contacts of Sudanese Patients with Pulmonary Tuberculosis in Eastern Sudan: Revisiting the Tuberculin Skin Test

Abstract

A third of the world’s population is latently infected with TB with an increased risk of developing active TB. Household contacts (HHCs) of pulmonary TB cases are at a greater risk of developing disease. Early identification and treatment of latent TB infected individuals may reduce progression to active TB. This study aimed to determine latent TB infections (LTBI) point prevalence among HHCs and community contacts (CCs) using Tuberculin Skin Test (TST) and whole blood IFN-γ release assay in an area of high TB prevalence. In a prospective, longitudinal and community-based study and following informed consent, 768 volunteers (HHCs n = 245; CCs n = 523) were enrolled. Tuberculin Skin Test (TST), whole blood stimulation with PPD and IFN-γ levels determination using ELISA were performed. Mean ages of HHCs and the CCs were not significantly different (HHCs 35.6 ± 15.7 and CCs 30.6 ± 11.7 years; p = 0.99), with a Male:Female ratio of 1:2. Mean recruitment TST indurations were 4.6 ± 5.5 mm and 2.8 ± 3 mm for HHCs and CCs respectively (p = 0.000). Follow-up (Day 614) mean TST indurations increased significantly to 9.1 ± 7.2 mm and 4.4 ± 3.2 mm for HHCs and CCs respectively (p = 0.001). Using TST indurations ≥ 10 mm, LTBI point prevalence for HHCs and CCs was significantly different (HHCs 461/1000 and 367/1000 individuals, p = 0.03). The mean IFN-γ levels for HHCs and CCs at recruitment day (Day 0) were 0.66 ± 0.17 IU/ml and 0.06 ± 0.04 respectively. The mean of IFN-γ production levels dropped significantly at Day 614 for HHCs and CCs to 0.66 ± 0.15 IU/ml and 0.02 ± 0.02 respectively (p = 0.03) (p = 0.00001). Recruitment LTBI point prevalence using IFN-γ level ≥ 0.35 IU/ml for HHCs and CCs was 440/1000 and 203/1000 respectively (p = 0.000000001). No correlations between TST indurations and IFN-γ levels were detected among HHCs or CCs (p > 0.05). TST is a simple, efficient and cheap technique for LTBI diagnosis and triaging individuals for treatment.