title: Regional differences regarding risk of developing rheumatoid arthritis in Stockholm County, Sweden: results from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study.
abstract: OBJECTIVE
  Rheumatoid arthritis (RA) is a complex disease that is associated with genetic and environmental factors. We have investigated geospatial variation in the risk of developing RA within Stockholm County, Sweden, with respect to established environmental risk factors for RA, as well as serologically defined subgroups of RA.
  
  
  METHODS
  Information regarding geographical location for 1432 cases and 2529 controls from the Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study, living in Stockholm County at RA symptom onset, or matched date for controls, was used to estimate geospatial variation in risk. We used generalized additive models (GAMs) to create a risk surface, calculate odds ratios (ORs), and adjust for potential confounding by smoking, education level, and RA within family. We performed a stratified analysis based on the presence/absence of anti-citrullinated peptide antibodies (ACPA).
  
  
  RESULTS
  We found significant spatial variation in the odds of developing RA in Stockholm County. After adjustment for smoking, education level, and family history of RA, this geospatial variation remained. The stratified analysis showed areas with higher ORs for ACPA-positive RA and ACPA-negative RA, after adjusting for smoking, education level, and having a family history of RA. Living in the city of Stockholm was associated with decreased risk of RA.
  
  
  CONCLUSIONS
  The risk of developing RA in Stockholm County is not distributed evenly and there are areas of increased risk that could not be explained by known factors. Further investigations of local exposures or social factors are warranted.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet , Stockholm , Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Källberg
authors.forename: V
authors.initials: V
authors.lastname: Vieira
authors.forename: M
authors.initials: M
authors.lastname: Holmqvist
authors.forename: J E
authors.initials: JE
authors.lastname: Hart
authors.forename: K H
authors.initials: KH
authors.lastname: Costenbader
authors.forename: C
authors.initials: C
authors.lastname: Bengtsson
authors.forename: L
authors.initials: L
authors.lastname: Klareskog
authors.forename: E W
authors.initials: EW
authors.lastname: Karlson
authors.forename: L
authors.initials: L
authors.lastname: Alfredsson
mesh_terms: D001172:Arthritis, Rheumatoid / Q000097:blood / Q000453:epidemiology*; D001323:Autoantibodies / Q000097:blood; D015415:Biomarkers / Q000097:blood; D004781:Environmental Exposure; D062665:Epidemiological Monitoring; D005260:Female; D062305:Geographic Mapping; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010456:Peptides, Cyclic / Q000276:immunology; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide