Associations of fire smoke and other pollutants with incident rheumatoid arthritis and rheumatoid arthritis-associated interstitial lung disease

Determine whether pollutants such as fire smoke-related particulate matter smaller than 2.5 microns (PM ) are associated with incident rheumatoid arthritis (RA) and RA-associated interstitial lung disease (RA-ILD). This case-control study used Veterans Affairs data 10/1/2009-12/31/2018. We identified incident RA and RA-ILD cases using validated algorithms, matching each case to up to 10 controls on age, gender, and VA enrollment year. We obtained pollutants including fire smoke PM , carbon monoxide, nitrogen oxides (NOx), ozone overall PM PM , and sulfur dioxide (SO ) at least one year before index date. We fit conditional logistic regression models to estimate adjusted odds ratios (aOR) with 95% confidence intervals (CI) for incident RA and RA-ILD, adjusted for confounders. We identified 9,701 incident RA cases (mean age 65, 86% male), including 531 RA-ILD cases (mean age 69, 91% male), and 68,852 matched controls. Fire smoke PM 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/m ). 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 PM (aOR 1.25, 95% CI 1.10-1.43) were associated with seronegative RA. Carbon monoxide, overall PM , and SO were not, or negatively, associated with RA and RA-ILD. Increased fire smoke PM was associated with RA-ILD, while NOx, ozone, and PM were associated with RA risk. Thus, air pollution may increase the risk of RA and RA-ILD.