Table 1

Characteristics of the EIRA cases and controls

CasesControls
N (%)14972536
 RF-positive982 (66%)N/A
 ACPA-positive991 (66%)N/A
 ACPA-negative505 (34%)N/A
Age at enrolment, mean (SD)51.5 (12.6)51.5 (12.6)
Gender (%)
 Male27.728.7
 Female72.371.3
Smoking status at enrolment (%)
 Never27.935.5
 Current26.918.6
 Non-regular10.510.0
 Former30.925.7
 Missing3.810.3
Education (%)
 Compulsory school21.816.1
 Vocational upper secondary school12.79.5
 Theoretical upper secondary school12.111.7
 Other education24.921.7
 University degree24.330.2
 Missing4.210.9
Air pollution in the 5th year before RA onset (median, IQR)
 PM10 (µg/m3)2.0 (2.6)2.1 (2.6)
 SO2 (µg/m3)1.7 (2.4)1.8 (2.2)
 NO2 (µg/m3)5.8 (7.5)5.6 (7.6)
Air pollution in the 10th year before RA onset (median, IQR)
 PM10 (µg/m3)1.9 (2.5)2.0 (2.5)
 SO2 (µg/m3)2.7 (3.7)2.4 (3.4)
 NO2 (µg/m3)7.4 (9.1)7.0 (9.1)
Air pollution in the 20th year before RA onset (median, IQR)
 PM10 (µg/m3)1.9 (2.3)1.9 (2.3)
 SO2 (µg/m3)9.1 (10.0)8.1 (9.3)
 NO2 (µg/m3)10.8 (12.9)10.4 (12.5)
Average air pollution (median, IQR)*
 PM10 (µg/m3)2.2 (2.0)2.3 (2.1)
 SO2 (µg/m3)7.7 (7.8)7.6 (8.4)
 NO2 (µg/m3)9.6 (8.8)9.7 (8.8)
  • *Average pollution calculated from the later of 1968 or date of birth to index date.

  • ACPA, anti-citrullinated protein antibody; EIRA, Epidemiological Investigation of Rheumatoid Arthritis; N/A, not applicable; RA, rheumatoid arthritis; RF, rheumatoid factor.