Fine Particulate Matter Constituents, Ozone, and Systemic Lupus Erythematosus: A Large General-Population Cohort Analysis With Extended Quantile g-Computation.

OBJECTIVE

The aim of this study was to investigate whether exposure to mixture of individual fine particulate matter (PM2.5) chemical constituents is associated with incident systemic lupus erythematosus (SLE) and if ozone modifies this association and/or is associated with SLE onset.

METHODS

We used MarketScan claims data to assemble a cohort of adults with at least two years' insurance coverage and no prior SLE diagnosis, with cohort entry defined as the first qualifying date. From this full cohort, we identified all people with incident SLE and a 20% random sample, yielding a case-cohort of 8.3 million people. Concentrations of ozone and seven PM2.5 constituents (ammonium, black carbon, mineral dust, sulfate, nitrate, organic matter, and sea salt) were estimated at the core-based statistical area/metropolitan-division level. Mean annual exposures for the two years before cohort entry were assigned to each person. Extended quantile g-computation produced hazard ratios (HRs) for the PM2.5 mixture and weights (ie, relative contributions to SLE onset) for individual constituents, adjusting for sex, age, chronic obstructive pulmonary disease, geographic region, and calendar year.

RESULTS

We identified 21,485 people with newly diagnosed SLE. At the median ozone level (36.15 parts per billion [ppb]), each quartile increase of PM2.5 mixture was associated with an HR of 1.14 (95% confidence interval [CI] 1.11-1.18) for SLE risk; mineral dust dominated this effect. Ozone was associated with SLE risk (HR 1.009 per 1 ppb, 95% CI 1.001-1.017). PM2.5's effect was particularly strong in settings of low ozone.

CONCLUSION

This study demonstrated how PM2.5 constituents (especially mineral dust) and ozone are associated with SLE incidence.