Evaluating 17 years of LTBI screening in NW England

Abstract

Introduction Rates of Tuberculosis (TB) in England remain comparatively high. About 72% of TB cases in the UK occur among non-UK born individuals, mostly as a result of reactivation of latent TB infection (LTBI). Programmatic screening for LTBI is a key intervention of the TB strategy for England. This paper aims to review the evidence of a long-standing LTBI screening initiative to shape and inform policy around LTBI screening. Methods A retrospective cohort was created through probabilistic linkage between LTBI screening data and TB case data from the Enhanced TB surveillance system in the UK. Persons screened for LTBI in Blackburn were followed up until they died, became a case, imputed emigration date or cohort end date (end of 2014). Incidence rates (IR) and incidence rate rations (IRRs) of TB were calculated in single and multi variable (Poisson regression) analysis. Results In total, 21 of the 1,341 individuals screened with QuantiFERON (QFT) between 2009 and 2013 and 76 of 479 screened with Tuberculin skin test (TST) between 1989-2001 were reported with active TB. Crude IRs amongst LTBI positive, treatment naive individuals were 4,900 per 100,000 person years (py) and 2,297 per 100,000 py in the QFT and TST cohorts respectively. Poisson regression showed that LTBI positivity (IRR 27.0, CI 8.5- 86.2) and no chemoprophylaxis (IRR 0.14, CI 0.04-0.5) were associated with becoming a case of TB. Conclusions Our observational study showed high TB rates among treatment naive individuals and a strong association between LTBI positivity and treatment and TB case notification. Demonstrating feasibility and effectiveness of LTBI screening, important policy lessons can be drawn for national LTBI screening in England and beyond.