Individual-level and country-level socioeconomic determinants of disease outcomes in SpA: multinational, cross-sectional study (ASAS-COMOSPA)

Objective To explore the independent contribution of individual-level and country level socioeconomic status (SES) determinants to disease activity and physical function in patients with spondyloarthritis (SpA).

Methods Data from the cross-sectional, multinational (n=22 countries worldwide) COMOSPA (COMOrbidities in SpA) study were used. Contribution of individual SES factors (gender, education) and country of residence to Ankylosing Spondylitis Disease Activity Score (ASDAS) and Bath Ankylosing Spondylitis Functional Index (BASFI) was explored in multilevel regression models, adjusting for clinical and demographic confounders. Next, the additional effects of national macroeconomic indicators (gross domestic product [GDP], Human Development Index, healthcare expenditure and Gini index) were explored. The mediating role of uptake of biologic disease-modifying antirheumatic drugs between education or GDP and ASDAS was explored by testing indirect effects.

Results In total, 3370 patients with SpA were included: 65% were male, with a mean age of 43 (SD 14), ASDAS of 2.0 (SD 1.1) and BASFI score of 3.1 (SD 2.7). In adjusted models, patients with low education and female patients had an OR of 1.7 (95% CI 1.3 to 2.2) and an OR of 1.7 (95% CI 1.4 to 2.0), respectively, of having ASDAS >= 2.1. They also reported slightly worse function. Large country differences were observed independent of individual SES and clinical confounders. Patients from less SES developed countries have worse ASDAS, while patterns for BASFI were insignificant. Uptake of biologicals did not mediate the relationship between individual-level or country-level SES and disease activity.

Conclusions Individual-level and country-level health inequalities exist also among patients with SpA. Women and lower educated persons had worse disease activity and somewhat worse physical function. While patients in less socioeconomically developed countries had higher disease activity, they reported similar physical function.