Cardiopulmonary hospitalization risks from wildfire and non-wildfire PM_2.5 in 20 US states

Given the increasing wildfire activity in the US, assessment of the health impacts of wildfire-specific fine particulate matter (PM_2.5), a growing source of surface air pollution, and its relative toxicity compared to non-wildfire PM_2.5 is needed to support mitigation strategies.

To investigate associations of long-term exposure of wildfire-specific and non-wildfire PM_2.5 with cardiopulmonary hospitalization risks.

We obtained over 89 million cardiopulmonary hospitalizations for residents across 20 US states from 2006 to 2019 from the State Inpatient Databases. We assigned estimated 2-year average concentrations of wildfire-specific and non-wildfire PM_2.5 to each hospitalization based on residential ZIP codes to characterize exposure levels. We used a self-controlled design, which is robust to unmeasured confounding, to assess the associations.

2-year moving average exposures to wildfire-specific and non-wildfire PM_2.5 from the year of hospitalization to the prior year.

The hospitalizations for cardiovascular (ischemic heart disease, cerebrovascular disease, heart failure, arrhythmia, other cardiovascular diseases) and pulmonary diseases (acute respiratory infections, pneumonia, chronic obstructive pulmonary disease [COPD], asthma, other respiratory diseases) were identified based on the first 3 diagnosis codes at discharge.

Wildfire-specific PM_2.5 had stronger effects than non-wildfire PM_2.5. Specifically, each 1-μg/m³ increase in 2-year wildfire-specific PM_2.5 was significantly associated with increased hospitalization risks for all cardiopulmonary diseases, with relative risk ranging from 1.100 (95% CI: 1.091, 1.108) for heart failure to 1.160 (95% CI: 1.142, 1.178) for asthma. In comparison, a 1 μg/m³ increase in non-wildfire PM_2.5 was associated with increased hospitalization risks for all cardiopulmonary diseases, but with relative risks ranging from 1.047 (95% CI: 1.042, 1.051) for COPD to 1.085 (95% CI: 1.082, 1.088) for hypertension. Stronger effects of both wildfire-specific and non-wildfire PM_2.5 were observed among minorities, individuals with obesity or diabetes, and those living in metropolitan areas, those with fewer years of education, and more deprived communities.

Long-term exposure to wildfire-specific PM_2.5 poses a greater risk of cardiopulmonary hospitalization than PM_2.5 from non-wildfire sources. Greater effort should be placed on wildfire management, with particular focus on strategies to reduce smoke in addition to traditional air quality control strategies.