Systemic Autoimmune Rheumatic Disease Risk: Association With Long-Term Exposure to Fine Particulate Matter.

Objective: Fine particulate matter (PM) is a possible trigger of systemic autoimmune rheumatic diseases (SARDs). We investigated SARDs risk related to long-term exposure to PM and its components (ammonium, black carbon, mineral dust, sea salt, nitrate, sulfate, organic matter), the composition of which may affect toxicity.

Methods: We assembled an open cohort of Quebec adults (without SARDs) using administrative health data from April 2000 to December 2019. Our SARD case definition included physician billing and hospitalization diagnostic codes for systemic lupus, dermatomyositis, systemic sclerosis, Sjögren disease, and undifferentiated connective tissue disease. Estimates of mean annual PM and its components were available from modeling using satellite aerosol optical depth images and ground-based observations. Exposures were assigned to each resident based on six-character postal codes, updated over time. Cox models (adjusted for age, sex, year, socioeconomic status, Local Service Network, and urban/rural region) generated hazard ratios (HRs) for PM and its seven components. Quantile-based g-computational models with similar adjustments were used to estimate marginal HRs for the mixture of PM components.

Results: We studied 7,482,397 Quebec residents. Over 98,039,305 person-years, 55,267 SARDs cases were identified. Using quantile g-computational models, the adjusted SARDs HR for a one-decile increase in PM components was 1.01 (95% confidence interval 1.00-1.02). Among the seven components, ammonium contributed most to SARDs risk.

Conclusion: This large general population cohort study suggests that ambient PM (and ammonium in particular) may be associated with SARDs incidence.