Interferon-gamma release assays for latent tuberculosis infection screening in Canadian federal correctional facilities

Abstract

BACKGROUND: The correctional setting presents an opportunity for latent TB infection (LTBI) screening in an otherwise difficult to reach demographic. We evaluate factors associated with the fidelity of the tuberculin skin test (TST) and interferon-gamma release assay (IGRA), specifically the QuantiFERON^®-TB Gold In-Tube assay (QFT-GIT), explain factors associated with discordance, and report LTBI treatment outcomes.METHODS: We describe the association between demographic and clinical variables, and predictors of concordance with IGRA using univariate logistic regression in a population of TST-positive inmates. We report outcomes among those offered LTBI treatment.RESULTS: We observed concordance between TST and QFT-GIT in 90 of 306 (29.4%) inmates. Persons with TST+/QFT-GIT+ results were less likely to be male (OR 3.94, 95% CI 1.73-8.97) or have a BCG vaccination history (OR 0.34, 95% CI 0.12-0.95), and more likely to be foreign-born (P < 0.001). Of the 108 inmates offered LTBI treatment, 65 (60.1%) accepted and 51 (78.0%) completed. TST/QFT-GIT discordance has not been associated with disease during follow-up.CONCLUSION: Our findings suggest that TST/QFT-GIT discordance in Canadian federal inmates is common; however, low-risk of disease progression in those with discordance suggests that a shift towards IGRA-based screening is warranted and feasible.