Mortality in US Hemodialysis Patients Following Exposure to Wildfire Smoke

Abstract

Significance Statement Wildfires generate high concentrations of fine particulate matter (PM 2.5 ), which are linked to increased morbidity and mortality. When inhaled, PM 2.5 can travel into the respiratory tract and trigger oxidative stress and systemic inflammation. Because of their frailty, patients with ESKD might be especially susceptible to this environmental stressor, but little is known about the effects of air pollution exposures in this population. In a retrospective cohort analysis, the authors found a 4% increase in daily mortality per 10- μ g/m 3 increase in wildfire PM 2.5 and a 7% increase in mortality over 30 days after exposure. On days with wildfire PM 2.5 >10 μ g/m 3 , fires accounted for 8.4% of daily mortality. The findings highlight an immediate and persistent effect of wildfire smoke on mortality among individuals receiving hemodialysis. Background 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. Methods 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. Results We found 48,454 deaths matched to the 253 counties. A 10- μ g/m 3 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 μ g/m 3 , exposure accounted for 8.4% of mortality. Conclusions Wildfire smoke exposure was positively associated with all-cause mortality among patients receiving in-center hemodialysis.

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