OR with 95% CI of developing rheumatoid arthritis (RA) for subjects exposed to passive smoking compared with those who have never been exposed, by duration of exposure
| Duration of exposure to passive smoking (years) | ACPA-positive RA | ACPA-negative RA | ||
| ca/co | OR (95% CI)* | ca/co | OR (95% CI)* | |
| 0 | 205/897 | 1.0 (reference) | 108/897 | 1.0 (reference) |
| 1–9 | 52/221 | 1.0 (0.7–1.5) | 18/221 | 0.7 (0.4–1.2) |
| 10–19 | 66/319 | 1.0 (0.7–1.3) | 33/319 | 0.9 (0.6–1.3) |
| 20- | 616/325 | 0.9 (0.7–1.3) | 45/325 | 1.1 (0.7–1.6) |
| P values for trend | 0.8 | 0.8 | ||
All subjects were never-smokers.
*Adjusted for age, gender, residential area and ancestry.
ACPA, anti-cyclic citrullinated peptide antibodies; ca/co, number of exposed cases and control.