Individual-level and country-level socio-economic factors and health outcomes in spondyloarthritis: analysis of the ASAS perSpA study

Objectives: The aim of this study was to investigate the association between individual-level and country-level socio-economic (SE) factors and health outcomes across SpA phenotypes. Methods: Patients with axial SpA (axSpA), peripheral SpA (pSpA) or PsA from the ASAS-perSpA study (in 23 countries) were included. The effect of individual-level (age, gender, education and marital status) and country-level [e.g. Gross Domestic Product (GDP)] SE factors on health outcomes [Ankylosing Spondylitis Disease Activity Score (ASDAS) ≥ 2.1, ASDAS, BASFI, fatigue and the Assessment of SpondyloArthritis international Society Health Index (ASAS-HI)] was assessed in mixed-effects models adjusted for potential confounders. Interactions between SE factors and disease phenotype were tested. A mediation analysis was conducted to explore whether the impact of country-level SE factors on ASDAS was mediated through biologic/targeted synthetic (b/ts) DMARD uptake. Results: In total, 4185 patients (61% males, mean age 45) were included (65% axSpA, 25% PsA, 10% pSpA). Female gender [β= 0.14 (95% CI: 0.06, 0.23)], lower educational level [β = 0.35 (0.25, 0.45)) and single marital status [β = 0.09 (0.01, 0.17)] were associated with higher ASDAS. Living in lower GDP countries was also associated with higher ASDAS [β = 0.39 (0.16, 0.63)], and 7% of this association was mediated by b/tsDMARD uptake. Higher BASFI was similarly associated with female gender, lower education and living alone, without the effect of country-level SE factors. Female gender and lower educational level were associated with worse ASAS-HI, while more fatigue was associated with female gender and higher country-level SE factors [lower GDP, β = -0.46 (-0.89 to -0.04)]. No differences across disease phenotypes were found. Conclusions: Our study shows country-driven variations in health outcomes in SpA, independently influenced by individual-level and country-level SE factors and without differences across disease phenotypes.