Nonlinear association between systemic immune-inflammation index (SII) and latent tuberculosis infection (LTBI) in U.S. adults: a study based on NHANES data from 2011-2012.

BACKGROUND: Although SII has been associated with various infectious and non-infectious conditions, its potential relevance to LTBI has not yet been comprehensively investigated. Therefore, this study aimed to investigate the relationship between SII and LTBI among U.S. adults by using data from the 2011-2012 National Health and Nutrition Examination Survey (NHANES). METHODS: This study used data from the 2011-2012 NHANES. To explore the relationship between SII and LTBI, weighted multivariable logistic regression models, smooth curve fitting, threshold effect analysis, subgroup analyses, and interaction tests were applied. RESULTS: A total of 4,398 participants were included in the analysis, of whom 520 were identified as having LTBI. An inverse association between Log2-SII and LTBI was observed in the fully adjusted model. A nonlinear association between Log2-SII and LTBI was also detected, with a potential inflection point of 7.51 (corresponding to an SII value of approximately 182.27). Further subgroup analyses and interaction tests showed no statistically significant interactions for sex, race/ethnicity, body mass index (BMI), smoking status, hypertension, diabetes, and history of household exposure to tuberculosis (TB) (all p for interaction > 0.05). CONCLUSION: The study identified that Log2-SII was nonlinearly and inversely associated with LTBI among U.S. adults. Notably, this association was evident at Log2-SII values greater than 7.51 (corresponding to an SII value of approximately 182.27), although further studies are warranted to validate this finding.