Cardiovascular and Cerebrovascular Emergency Department Visits Associated With Wildfire Smoke Exposure in California in 2015

Abstract

Background: Wildfire smoke is known to exacerbate respiratory conditions; however, evidence for cardiovascular and cerebrovascular events has been inconsistent, despite biological plausibility.

Methods and results: A population-based epidemiologic analysis was conducted for daily cardiovascular and cerebrovascular emergency department (ED) visits and wildfire smoke exposure in 2015 among adults in 8 California air basins. A quasi-Poisson regression model was used for zip code-level counts of ED visits, adjusting for heat index, day of week, seasonality, and population. Satellite-imaged smoke plumes were classified as light, medium, or dense based on model-estimated concentrations of fine particulate matter. Relative risk was determined for smoky days for lag days 0 to 4. Rates of ED visits by age- and sex-stratified groups were also examined. Rates of all-cause cardiovascular ED visits were elevated across all lags, with the greatest increase on dense smoke days and among those aged ≥65 years at lag 0 (relative risk 1.15, 95% confidence interval [1.09, 1.22]). All-cause cerebrovascular visits were associated with smoke, especially among those 65 years and older, (1.22 [1.00, 1.49], dense smoke, lag 1). Respiratory conditions were also increased, as anticipated (1.18 [1.08, 1.28], adults >65 years, dense smoke, lag 1). No association was found for the control condition, acute appendicitis. Elevated risks for individual diagnoses included myocardial infarction, ischemic heart disease, heart failure, dysrhythmia, pulmonary embolism, ischemic stroke, and transient ischemic attack.

Conclusions: Analysis of an extensive wildfire season found smoke exposure to be associated with cardiovascular and cerebrovascular ED visits for all adults, particularly for those over aged 65 years.

Keywords: heart failure; ischemic heart disease; particulate matter; stroke; wildfire.

Figure 1

Total number of days with any smoke plumes by county from May 1 through September 30, 2015. California air basins in the study region are labeled and outlined in black, those excluded in gray.

Figure 2

Relative risk and 95% confidence intervals for select cardiovascular, cerebrovascular, and respiratory outcomes relative to smoke‐free days, at lag 0 days, stratified by age; 8 California air basins (May 1–September 30, 2015). Models adjusted for heat index, day of week, time trend, and log‐population offset. RR indicates relative risk.

Figure 3

Relative risk and 95% confidence intervals for select cardiovascular, cerebrovascular, respiratory, and control outcomes relative to smoke‐free days, across lags 0 to 4 days, adults aged ≥65 years, 8 California air basins (May 1–September 30, 2015). Models adjusted for heat index, day of week, time trend, and log‐population offset. RR indicates relative risk.