Blazing a Trail Against Wildfires

Wildfires across the US are increasing in frequency and ferocity, and where there is fire, there is smoke. Wildfire smoke is dense, toxic, and carries harmful pollutants up to hundreds of miles away.¹ “Wildfire smoke increasingly affects my patients, even practicing as I do in the Northeast,” said Tess Wiskel, an emergency medicine physician and faculty member at Harvard Medical School.

Numerous studies have linked wildfire smoke exposure to respiratory complications, including bronchitis, asthma, and other breathing difficulties that require hospitalization.² However, it is less clear how smoke exposure affects cardiovascular events. A recent study published in the Journal of the American Heart Association added another piece to this puzzle with insights into how behavioral modifications might mitigate the health impacts of smoke exposure.³

Jamal Rana, a physician-scientist and chief of cardiology at Kaiser Permanente’s Oakland Medical Center, and his team examined cardiovascular hospitalization and death rates among 3.2 million adults in Northern California between July 1 and December 31, 2018. The study period included two large wildfires. In July 2018, the Mendocino Complex fire burned 459,000 acres and released dense smoke for two months. Three months later, the Camp fire consumed fewer acres but released an even denser smoke plume lasting two weeks. As expected, both fires created a sudden, sharp spike in fine particulate matter (PM2.5, the most harmful component of wildfire smoke) well above the recommended threshold for air pollution. On days unaffected by wildfires, PM2.5 levels remained low.

Rana and his team found that high PM2.5 during the Mendocino Complex fire was associated with statistically significant health impacts. They discovered 23.1 percent more cardiovascular events and a 35.8 percent increase in mortality compared to days when PM2.5 was in the “Good” range of the United States Environmental Protection Agency Air Quality Index categories. However, there was no significant increase in either endpoint following the Camp fire. “This finding surprised us,” said Stacey Alexeeff, a biostatistician at Kaiser Permanente Division of Research and first author of this study. “Both fires led to air quality above the daily limit set to protect public health. In fact, there was one day when the Camp fire was responsible for the worst air pollution in the world.”

To help make sense of these results, the researchers probed Google search trends during the two wildfires. They found that searches for “wildfire smoke”, “air quality”, and “N95 mask” increased slightly during the Mendocino complex fire, but they skyrocketed following the Camp fire— the highest ever reported for these three search terms.

This study may provide insight into how the public’s assessment of risk influences their behavior and health. Perhaps the Camp fire’s denser smoke plume encouraged individuals to take more precautions. Or perhaps people were primed by the Mendocino Complex fire and learned how to avoid smoke exposure and improve indoor air quality. Or were there more public service announcements or school closures during the Camp fire? “It’s possible that people did more to protect themselves during the Camp fire because of all the public health messages they heard,” Alexeeff said.

While the precise nature of the relationship between wildfire smoke and cardiovascular health remains unclear, this study supports educational and behavioral interventions for strengthening community resilience during wildfires. “The power of this study is through provocation. We need more research to answer this question: why was high particulate matter associated with cardiovascular disease and death on some days and not others?” Wiskel said.

Future studies that investigate both the effect of smoke on health and the potential for behavioral changes to mitigate adverse impacts will be crucial in protecting communities and vulnerable individuals in the years to come.