Determinants of QuantiFERON Plus-diagnosed tuberculosis infection in adult Ugandan TB contacts: A cross-sectional study

Background The tuberculin skin test is commonly used to diagnose latent tuberculosis infection (LTBI) in resource-limited settings, but its specificity is limited by factors including cross-reactivity with BCG vaccine and environmental mycobacteria. Interferon-gamma release assays (IGRA) overcome this problem by detecting M. tuberculosis complex-specific responses, but studies to determine risk factors for IGRA-positivity in high TB burden settings are lacking. Methods We conducted a cross-sectional study to determine factors associated with a positive IGRA by employing the QuantiFERON-TB® Gold-plus (QFT Plus) assay in a cohort of asymptomatic adult TB contacts in Kampala, Uganda. Multivariate logistic regression analysis with forward stepwise logit function was employed to identify independent correlates of QFT Plus-positivity. Results Of the 202 participants enrolled, 129/202 (64%) were female, 173/202 (86%) had a BCG scar, and 67/202 (33%) were HIV-infected. Overall, 105/192 (54%, 95% CI 0.48–0.62) participants had a positive QFT Plus result. Increased risk of QFT-Plus positivity was independently associated with manual employment/unemployment vs. professional employment (adjusted odds ratio (aOR) 2.18, 95% CI 1.01–4.72), a family vs. non-family relation to the index patient (aOR 2.87, 95% CI 1.33–6.18), living in the same vs. a different house as the index (aOR 3.05, 95% CI 1.28–7.29), a higher body mass index (BMI) (aOR per additional kg/m2 1.09, 95% CI 1.00–1.18) and tobacco smoking vs. not (aOR 2.94, 95% CI 1.00–8.60). HIV infection was not associated with QFT-Plus positivity (aOR 0.91, 95% CI 0.42–1.96). Conclusion The prevalence of IGRA positivity in this study population was lower than previously estimated. Tobacco smoking and raised BMI are hitherto unappreciated determinants of LTBI risk in this setting.ExcelFunding provided by: Wellcome TrustCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010269Award Number: 107742/Z/15/ZA cross-sectional study to determine factors associated with a positive IGRA by employing the QuantiFERON-TB® Gold-plus (QFT Plus) assay in a cohort of asymptomatic adult TB contacts in Kampala, Uganda. Multivariate logistic regression analysis with forward stepwise logit function was employed to identify independent correlates of QFT Plus-positivity