title: Lower education and living in countries with lower wealth are associated with higher disease activity in rheumatoid arthritis: results from the multinational COMORA study.
abstract: OBJECTIVE
  To investigate the relationship of socioeconomic status (SES) on an individual and country level with disease activity in rheumatoid arthritis (RA) and explore the mediating role of uptake of costly biological disease-modifying antirheumatic drugs (bDMARDs) in this relationship.
  
  
  METHODS
  Data from a cross-sectional multinational study (COMOrbidities in RA) were used. Contribution of individual socioeconomic factors and country of residence to disease activity score with 28-joint assessment (DAS28) was explored in regression models, adjusting for relevant clinical confounders. Next, country of residence was replaced by gross domestic product (GDP) (low vs high) to investigate the contribution of SES by comparing R(2) (model fit). The mediating role of uptake of bDMARDs in the relationship between education or GDP and DAS28 was explored by testing indirect effects.
  
  
  RESULTS
  In total, 3920 patients with RA were included (mean age 56 (SD 13) years, 82% women, mean DAS28 3.7 (1.6)). After adjustment, women (vs men) and low-educated (vs university) patients had 0.35 higher DAS28. Adjusted country differences in DAS28, compared with the Netherlands (lowest DAS28), varied from +0.2 (France) to +2.4 (Egypt). Patients from low GDP countries had 0.98 higher DAS28. No interactions between individual-level and country-level variables were observed. A small mediation effect of uptake of bDMARDs in the relationship between education and DAS28 (7.7%) and between GDP and DAS28 (6.7%) was observed.
  
  
  CONCLUSIONS
  Female gender and lower individual or country SES were independently associated with DAS28, but did not reinforce each other. The association between lower individual SES (education) or lower country welfare (GDP) with higher DAS28 was partially mediated by uptake of bDMARDs.
authors: Department of Internal Medicine, Division of Rheumatology, Maastricht University Medical Center and CAPHRI, Maastricht University, Maastricht, the Netherlands Health Promotion, CAPHRI, Maastricht University, Maastricht, the Netherlands.
authors: Polina
authors: P
authors: Putrik
authors: Department of Clinical Immunology & Rheumatology, Amsterdam Rheumatology Center, University of Amsterdam, Amsterdam, the Netherlands Department of Rheumatology, Hospital Garcia de Orta, Almada, Portugal.
authors: Sofia
authors: http://orcid.org/0000-0002-8899-9087
authors: S
authors: Ramiro
authors: Department of Medical Informatics, Uniklinik RWTH Aachen University, Aachen, Germany.
authors: Andras P
authors: AP
authors: Keszei
authors: Mohammed V University, Faculty of Medicine, Laboratory of Clinical Research and Epidemiology, Rheumatology Department, El Ayachi Hospital, Rabat, Morocco.
authors: Ihsane
authors: http://orcid.org/0000-0003-4402-5034
authors: I
authors: Hmamouchi
authors: Paris Descartes University, Rheumatology Department, Cochin Hospital, Assistance Publique-Hôpitaux de Paris, INSERM (U1153): Clinical Epidemiology and Biostatistics, PRES Sorbonne Paris-Cité, France.
authors: Maxime
authors: M
authors: Dougados
authors: National Advisory Unit on Rehabilitation in Rheumatology, Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors: Till
authors: T
authors: Uhlig
authors: Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors: Tore K
authors: TK
authors: Kvien
authors: Department of Internal Medicine, Division of Rheumatology, Maastricht University Medical Center and CAPHRI, Maastricht University, Maastricht, the Netherlands.
authors: Annelies
authors: A
authors: Boonen
mesh_terms: D000328:Adult; D000368:Aged; D018501:Antirheumatic Agents / Q000627:therapeutic use; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000453:epidemiology / Q000503:physiopathology*; D003430:Cross-Sectional Studies; D004522:Educational Status; D004534:Egypt; D005260:Female; D005602:France; D059066:Gross Domestic Product; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D012111:Residence Characteristics; D012720:Severity of Illness Index; D012737:Sex Factors; D012923:Social Class
chemical_list: D018501:Antirheumatic Agents
keywords: DAS28; Epidemiology; Rheumatoid Arthritis