Wildfire smoke has acute cardiorespiratory impact, but long-term effects still under study


Research on health impact

In early June of 2008, Wayne Cascio, MD, awoke in his Greenville, N.C., home to the stench of smoke emanating from a large peat fire burning some 65 miles away. By the time he reached the parking lot at East Carolina University in Greenville to begin his workday as chief of cardiology, the haze of smoke had thickened to the point where he could only see a few feet in front of him.

Dr. Wayne Cascio is director of the EPA's National Health and Environmental Effects Research Laboratory.

Dr. Wayne Cascio

Over the next several weeks, the fire scorched 41,000 acres and produced haze and air pollution that far exceeded National Ambient Air Quality Standards for particulate matter and blanketed rural communities in the state’s eastern region. The price tag for management of the blaze reached $20 million. Because of his interest in the health effects of wildfire smoke and because of his relationship with investigators at the EPA, Dr. Cascio initiated an epidemiology study to investigate the effects of exposure on cardiorespiratory outcomes in the population affected by the fire (Environ Health Perspect. 2011 Oct;119[10]:1415-20).

By combining satellite data with syndromic surveillance drawn from hospital records in 41 counties contained in the North Carolina Disease Event Tracking and Epidemiologic Collection Tool, he and his colleagues found that exposure to the peat wildfire smoke led to increases in the cumulative risk ratio for asthma (relative risk, 1.65), chronic obstructive pulmonary disease (RR, 1.73), and pneumonia and acute bronchitis (RR, 1.59). ED visits related to cardiopulmonary symptoms and heart failure also were significantly increased (RR, 1.23 and 1.37, respectively). “That was really the first study to strongly identify a cardiac endpoint related to wildfire smoke exposure,” said Dr. Cascio, who now directs the EPA’s National Health and Environmental Effects Research Laboratory. “It really pointed out how little we knew about the health effects of wildfire up until that time.”

Those early findings have been replicated in subsequent research about the acute health effects of exposure to wildfire smoke, which contains PM2.5 and other toxic substances from structures, electronic devices, and automobiles destroyed in the path of flames, including heavy metals and asbestos. Most of the work has focused on smoke-related cardiovascular and respiratory ED visits and hospitalizations.

A study of the 2008 California wildfire impact on ED visits accounted for ozone levels in addition to PM2.5 in the smoke. During the active fire periods, PM2.5 was significantly associated with exacerbations of asthma and COPD and these effects remained after controlling for ozone levels. PM2.5 inhalation during the wildfires was associated with increased risk of an ED visit for asthma (RR, 1.112; 95% confidence interval, 1.087-1.138) for a 10 mcg/m3 increase in PM2.5 and COPD (RR, 1.05; 95% CI, 1.019-1.0825), as well as for combined respiratory visits (RR, 1.035; 95% CI, 1.023-1.046) (Environ Int. 2109 Aug;129:291-8).

Researchers who evaluated the health impacts of wildfires in California during the 2015 fire season found an increase in all-cause cardiovascular and respiratory ED visits, especially among those aged 65 years and older during smoke days. The population-based study included 1,196,233 ED visits during May 1–Sept. 30 that year. PM2.5 concentrations were categorized as light, medium, or dense. Relative risk rose with the amount of smoke in the air. Rates of all-cause cardiovascular ED visits were elevated across levels of smoke density, with the greatest increase on dense smoke days and among those aged 65 years or older (RR,1.15; 95% CI, 1.09-1.22). All-cause cerebrovascular visits were associated with dense smoke days, especially among those aged 65 years and older (RR, 1.22; 95% CI, 1.00-1.49). Respiratory conditions also were increased on dense smoke days (RR, 1.18; 95% CI, 1.08-1.28) (J Am Heart Assoc. 2018 Apr 11;7:e007492. doi: 10.1161/JAHA.117.007492).


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