Wildfire, evacuation, and cardiovascular events: A spatial exposure approach

Increasingly, adverse health effects from wildfire exposure are not limited to select populations in the wildlandurban interface. As wildfires continue to grow in frequency and intensity, they are also continuing to encroach on urban areas, putting larger and larger populations at risk. In this study we develop an innovative research design in the wildfire and health literature, and report results for a small scale implementation on California's central coast. Instead of focusing on smoke exposure and PM 2.5 or PM 10 as the primary physiological pathway linking wildfire and adverse cardiovascular health outcomes, we draw on a stress pathway as a potential link between stress and heart health. We use a novel spatiotemporal definition of wildfire exposure that is directly measurable at the individual level and acutely stressful: evacuation orders. Combining longitudinal health data from the dominant local hospital system in southern Santa Barbara County, California, we directly determine exposure to an evacuation order and smoke plumes from three large fires in the 2017-2019 wildfire period. Controlling for additional known risk factors, such as diabetes status and smoking status, we model the risk of secondary cardiovascular events (CVE) for 2411 patients with existing cardiovascular disease. Roughly 16.2% of patients (n = 391) were exposed to an evacuation order. We found evacuation order exposure was not significantly associated with an increased risk of cardiac events for the CVD population, but estimates hovered between 12.5 and 16.3% over un-evacuated cohorts. Smoke exposures were not significantly associated with CVE risk in models adjusted for evacuation orders nor unadjusted models, and estimates of effects varied widely. Both the method and the findings have implications for public health departments, clinicians and wildfire researchers.