Mortality in US Hemodialysis Patients Following Exposure to Wildfire Smoke.

Abstract

Wildfires are increasingly a significant source of fine particulate matter (PM_2.5), which has been linked to adverse health effects and increased mortality. ESKD patients are potentially susceptible to this environmental stressor. We conducted a retrospective time-series analysis of the association between daily exposure to wildfire PM_2.5 and mortality in 253 counties near a major wildfire between 2008 and 2012. Using quasi-Poisson regression models, we estimated rate ratios (RRs) for all-cause mortality on the day of exposure and up to 30 days following exposure, adjusted for background PM_2.5, day of week, seasonality, and heat. We stratified the analysis by causes of death (cardiac, vascular, infectious, or other) and place of death (clinical or nonclinical setting) for differential PM_2.5 exposure and outcome classification. We found 48,454 deaths matched to the 253 counties. A 10-<i>μ</i>g/m³ increase in wildfire PM_2.5 associated with a 4% increase in all-cause mortality on the same day (RR, 1.04; 95% confidence interval [95% CI], 1.01 to 1.07) and 7% increase cumulatively over 30 days following exposure (RR, 1.07; 95% CI, 1.01 to 1.12). Risk was elevated following exposure for deaths occurring in nonclinical settings (RR, 1.07; 95% CI, 1.02 to 1.12), suggesting modification of exposure by place of death. "Other" deaths (those not attributed to cardiac, vascular, or infectious causes) accounted for the largest portion of deaths and had a strong same-day effect (RR, 1.08; 95% CI, 1.03 to 1.12) and cumulative effect over the 30-day period. On days with a wildfire PM_2.5 contribution >10 <i>μ</i>g/m³, exposure accounted for 8.4% of mortality. Wildfire smoke exposure was positively associated with all-cause mortality among patients receiving in-center hemodialysis.