Canadian Wildfires of 2023 and Risk of Mortality and Hospitalization among ESKD Patients

Background: Climate change driven droughts are increasing frequency and intensity of wildfires, a significant source of air pollution. Smoke plumes from the 2023 Canadian wildfires travelled long distances and negatively impacted air quality across large swaths of eastern US. We investigated the association between exposure to 2023 Canadian wildfire-related air pollutants and risk of mortality and hospitalization among hemodialysis patients in New England, the Mid-Atlantic, and the Midwest U.S. Methods: The study population includes the end stage kidney disease patients (N=52,995) receiving hemodialysis treatment at Fresenius Kidney Care clinics located in New England, the Mid-Atlantic, and the Midwest U.S. during June-July 2023. Daily number of all-cause deaths, all-cause hospitalizations, respiratory disease hospitalizations, and cardiovascular disease hospitalizations were counted for each hemodialysis clinic. Presence and absence of wildfire smoke plume and wildfire-related fine particulate matter (PM2.5) concentration were assessed using both satellite-derived smoke polygons and ground-based PM2.5 monitors. We constructed a retrospective observational study using a time-stratified case-crossover analysis with a conditional quasi-Poisson model to investigate the risk of mortality and hospitalization associated with exposures to wildfire-related air pollutants. Results: Canadian wildfires of 2023 significantly increased air pollution level across the dialysis clinics in the study area, with the highest daily wildfire-related PM2.5 concentration reaching 251.1µg/m3. The presence of wildfire smoke plume was associated with an 18% increase in risk of same day (lag0) all-cause mortality (rate ratio [RR]:1.18; 95% confidence interval [CI], 1.13-1.24) and a 3% increase in risk of all-cause hospitalization (RR:1.03; 95% CI, 1.00-1.07). A 10-μg/m3 increase in wildfire-related PM2.5 was associated with a 139% increase in same day all-cause mortality (RR: 2.39; 95% CI, 1.79-3.18), and a 33% increase in all-cause hospitalization (RR:1.33; 95% CI, 1.10-1.62). Conclusion: Our data suggest that air pollution from the 2023 Canadian wildfires resulted in increased risk of mortality and hospitalization among hemodialysis patients in New England, the Mid-Atlantic, and the Midwest U.S.