Associations of Fire Smoke and Other Pollutants With Incident Rheumatoid Arthritis and Rheumatoid Arthritis–Associated Interstitial Lung Disease

Objective: The aim of this study was to determine whether pollutants such as fire smoke–related particulate matter <2.5 μm (PM_2.5) are associated with incident rheumatoid arthritis (RA) and RA-associated interstitial lung disease (RA-ILD). Methods: This patient–control study used Veterans Affairs (VA) data from October 1, 2009, to December 31, 2018. We identified patients with incident RA and RA-ILD using validated algorithms, matching each patient to ≤10 controls on age, sex, and VA enrollment year. We obtained pollutants including fire smoke PM_2.5, carbon monoxide, nitrogen oxides (NOx), ozone, overall PM_2.5, PM₁₀, and sulfur dioxide (SO₂) at least one year before the index date. We fit conditional logistic regression models to estimate adjusted odds ratios (aORs) with 95% confidence intervals (CIs) for incident RA and RA-ILD, adjusted for confounders. Results: We identified 9,701 patients with incident RA (mean age 65 years, 86% male), including 531 patients with RA-ILD (mean age 69 years, 91% male), and 68,852 matched controls. Fire smoke PM_2.5 was not associated with RA (aOR 1.07, 95% CI 0.92–1.23) but was associated with RA-ILD (aOR 1.98, 95% CI 1.08–3.62, per 1 μg/m³). Increased levels of NOx were associated with RA (aOR 1.16, 95% CI 1.06–1.27, highest vs lowest quartile). The highest quartiles of ozone (aOR 1.19, 95% CI 1.06–1.34) and PM₁₀ (aOR 1.25, 95% CI 1.10–1.43) were associated with seronegative RA. Carbon monoxide, overall PM_2.5, and SO₂ were not, or negatively, associated with RA and RA-ILD. Conclusion: Increased fire smoke PM_2.5 was associated with RA-ILD, whereas NOx, ozone, and PM₁₀ were associated with RA risk. Thus, air pollution may increase the risk of RA and RA-ILD. (Figure presented.).