Long-term exposure to wildfire-specific fine particulate matter could be associated with greater cardiopulmonary hospitalization risk with equivalent concentration increase compared with exposure to fine particulate matter from nonwildfire sources.
Investigators used a self-controlled design to analyze 57.3 million cardiovascular and 32.7 million pulmonary hospitalizations across 20 US states from 2006 to 2019. Residential ZIP codes were linked to modeled wildfire-specific and nonwildfire-specific fine particulate matter (PM2.5) concentrations, with long-term exposure based on 2-year averages encompassing the hospitalization year and preceding year. The investigators compared exposure during hospitalization years with exposure during control years for the same hospitalization, accounting for time-invariant confounders while adjusting for measured time-varying factors.
They evaluated hospitalizations for ischemic heart disease, cerebrovascular disease, heart failure, arrhythmia, hypertension, other cardiovascular diseases, acute respiratory infections, pneumonia, chronic obstructive pulmonary disease (COPD), asthma, and other respiratory diseases. They assessed hospitalization risk associated with each 1-µg/m³ increase in the 2-year average concentration of wildfire-specific and nonwildfire PM2.5 and examined differences according to patient characteristics, comorbidities, disease severity, and neighborhood-level factors.
Each 1-µg/m³ increase in wildfire-specific PM2.5 was associated with increased hospitalization risk across all cardiopulmonary conditions. Cardiovascular risk increases ranged from 10% for heart failure to 13% for cerebrovascular disease. Among pulmonary conditions, asthma had the largest increase at 16%, while pneumonia was associated with an 11% increase.
Nonwildfire PM2.5 was also associated with increased hospitalization risk across the conditions studied, but the increases per 1-µg/m³ exposure were smaller. Cardiovascular risk increases ranged from about 5% for arrhythmia to 9% for hypertension, while pulmonary risk increases ranged from about 5% for COPD to 7% for other respiratory diseases.
Annual mean wildfire-specific PM2.5 was 0.29 µg/m³ compared with 7.78 µg/m³ for nonwildfire PM2.5, and 2-year average concentrations of nonwildfire PM2.5 were up to 27 times higher. When the investigators evaluated increases based on the standard deviation of each exposure, cardiopulmonary hospitalization risk increases were greater for nonwildfire PM2.5. They noted that this approach may better represent the relative magnitude of exposure changes in real-world settings.
Subgroup analyses suggested greater PM2.5-associated hospitalization risks among racial and ethnic minorities, as well as among patients living in metropolitan areas and communities with lower educational attainment or greater deprivation. Patients with obesity or diabetes also had greater risks across most cardiopulmonary conditions.
The study had several limitations. Wildfire-specific PM2.5 was estimated using a model with limited spatial resolution and predictive performance, potentially introducing exposure measurement error. Estimating nonwildfire PM2.5 by subtracting wildfire-specific PM2.5 from total PM2.5 introduced another potential source of measurement error. The investigators included just 20 states with varying observation periods, and the data lacked unique patient identifiers, preventing them from identifying repeat hospitalizations. Residual confounding from time-varying behaviors, indoor exposures, drug use, copollutants, and differences between ambient and personal exposure also remained possible.
“[A]t an equivalent concentration increase, long-term exposure to wildfire-specific PM2.5 poses a greater risk of cardiopulmonary hospitalization than nonwildfire PM2.5,” wrote lead study author Min Zhang, of the Icahn School of Medicine at Mount Sinai and Harvard T.H. Chan School of Public Health, and colleagues.
The study authors declared no conflicts of interest.
Source: Nature Communications