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

Abstract

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.