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The 2019 wildfire season is underway in many locales across the United States, exposing millions of individuals to smoky conditions that will have health consequences ranging from stinging eyes to scratchy throats to a trip to the ED for asthma or chronic obstructive pulmonary disease (COPD) exacerbation. Questions about long-term health impacts are on the minds of many, including physicians and their patients who live with cardiorespiratory conditions.
John R. Balmes, MD, a pulmonologist at the University of California, San Francisco, and an expert on the respiratory and cardiovascular effects of air pollutants, suggested that the best available published literature points to “pretty strong evidence for acute effects of wildfire smoke on respiratory health, meaning people with preexisting asthma and COPD are at risk for exacerbations, and probably for respiratory tract infections as well.” He said, “It’s a little less clear, but there’s good biological plausibility for increased risk of respiratory tract infections because when your alveolar macrophages are overloaded with carbon particles that are toxic to those cells, they don’t function as well as a first line of defense against bacterial infection, for example.”
The new normal of wildfires
Warmer, drier summers in recent years in the western United States and many other regions, attributed by climate experts to global climate change, have produced catastrophic wildfires (PNAS;2016 Oct 18;113[42]11770-5; Science 2006 Aug 18;313:940-3). The Camp Fire in Northern California broke out in November 2018, took the lives of at least 85 people, and cost more than $16 billion in damage. Smoke from that blaze reached hazardous levels in San Francisco, Sacramento, Fresno, and many other smaller towns. Other forest fires in that year caused heavy smoke conditions in Portland, Seattle, Vancouver, and Anchorage. Such events are expected to be repeated often in the coming years (Int J Environ Res Public Health. 2019 Jul 6;16[13]). 
Wildfire smoke can contain a wide range of substances, chemicals, and gases with known and unknown cardiorespiratory implications. “Smoke is composed primarily of carbon dioxide, water vapor, carbon monoxide, particulate matter, hydrocarbons and other organic chemicals, nitrogen oxides, trace minerals and several thousand other compounds,” according to the U.S. Environmental Protection Agency (Wildfire smoke: A guide for public health officials 2019. Washington, D.C.: EPA, 2019). The EPA report noted, “Particles with diameters less than 10 mcm (particulate matter, or PM10) can be inhaled into the lungs and affect the lungs, heart, and blood vessels. The smallest particles, those less than 2.5 mcm in diameter (PM2.5), are the greatest risk to public health because they can reach deep into the lungs and may even make it into the bloodstream.”
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.
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).
Long-term effects unknown
When it comes to the long-term effects of wildfire smoke on human health outcomes, much less is known. In a recent literature review, Colleen E. Reid, PhD, and Melissa May Maestas, PhD, found only one study that investigated long-term respiratory health impacts of wildfire smoke, and only a few studies that have estimated future health impacts of wildfires under likely climate change scenarios (Curr Opin Pulm Med. 2019 Mar;25:179-87).
“We know that there are immediate respiratory health effects from wildfire smoke,” said Dr. Reid of the department of geography at the University of Colorado Boulder. “What’s less known is everything else. That’s challenging, because people want to know about the long-term health effects.”
Evidence from the scientific literature suggests that exposure to air pollution adversely affects cardiovascular health, but whether exposure to wildfire smoke confers a similar risk is less clear. “Until just a few years ago we haven’t been able to study wildfire exposure measures on a large scale,” said EPA scientist Ana G. Rappold, PhD, a statistician there in the environmental public health division of the National Health and Environmental Effects Research Laboratory. “It’s also hard to predict wildfires, so it’s hard to plan for an epidemiologic study if you don’t know where they’re going to occur.”
Dr. Rappold and colleagues examined cardiopulmonary hospitalizations among adults aged 65 years and older in 692 U.S. counties within 200 km of 123 large wildfires during 2008-2010 (Environ Health Perspect. 2019;127[3]:37006. doi: 10.1289/EHP3860). They observed that an increased risk of PM2.5-related cardiopulmonary hospitalizations was similar on smoke and nonsmoke days across multiple lags and exposure metrics, while risk for asthma-related hospitalizations was higher during smoke days. “One hypothesis is that this was an older study population, so naturally if you’re inhaling smoke, the first organ that’s impacted in an older population is the lungs,” Dr. Rappold said. “If you go to the hospital for asthma, wheezing, or bronchitis, you are taken out of the risk pool for cardiovascular and other diseases. That could explain why in other studies we don’t see a clear cardiovascular signal as we have for air pollution studies in general. Another aspect to this study is, the exposure metric was PM2.5, but smoke contains many other components, particularly gases, which are respiratory irritants. It could be that this triggers a higher risk for respiratory [effects] than regular episodes of high PM2.5 exposure, just because of the additional gases that people are exposed to.”
Another complicating factor is the paucity of data about solutions to long-term exposure to wildfire smoke. “If you’re impacted by high-exposure levels for 60 days, that is not something we have experienced before,” Dr. Rappold noted. “What are the solutions for that community? What works? Can we show that by implementing community-level resilience plans with HEPA [high-efficiency particulate air] filters or other interventions, do the overall outcomes improve? Doctors are the first ones to talk with their patients about their symptoms and about how to take care of their conditions. They can clearly make a difference in emphasizing reducing exposures in a way that fits their patients individually, either reducing the amount of time spent outside, the duration of exposure, and the level of exposure. Maybe change activities based on the intensity of exposure. Don’t go for a run outside when it’s smoky, because your ventilation rate is higher and you will breathe in more smoke. Become aware of those things.”
Advising vulnerable patients
While research in this field advances, the unforgiving wildfire season looms, assuring more destruction of property and threats to cardiorespiratory health. “There are a lot of questions that research will have an opportunity to address as we go forward, including the utility and the benefit of N95 masks, the utility of HEPA filters used in the house, and even with HVAC [heating, ventilation, and air conditioning] systems,” Dr. Cascio said. “Can we really clean up the indoor air well enough to protect us from wildfire smoke?”
The way he sees it, the time is ripe for clinicians and officials in public and private practice settings to refine how they distribute information to people living in areas affected by wildfire smoke. “We can’t force people do anything, but at least if they’re informed, then they understand they can make an informed decision about how they might want to affect what they do that would limit their exposure,” he said. “As a patient, my health care system sends text and email messages to me. So, why couldn’t the hospital send out a text message or an email to all of the patients with COPD, coronary disease, and heart failure when an area is impacted by smoke, saying, ‘Check your air quality and take action if air quality is poor?’ Physicians don’t have time to do this kind of education in the office for all of their patients. I know that from experience. But if one were to only focus on those at highest risk, and encourage them to follow our guidelines, which might include doing HEPA filter treatment in the home, we probably would reduce the number of clinical events in a cost-effective way.”
The 2019 wildfire season is underway in many locales across the United States, exposing millions of individuals to smoky conditions that will have health consequences ranging from stinging eyes to scratchy throats to a trip to the ED for asthma or chronic obstructive pulmonary disease (COPD) exacerbation. Questions about long-term health impacts are on the minds of many, including physicians and their patients who live with cardiorespiratory conditions.
John R. Balmes, MD, a pulmonologist at the University of California, San Francisco, and an expert on the respiratory and cardiovascular effects of air pollutants, suggested that the best available published literature points to “pretty strong evidence for acute effects of wildfire smoke on respiratory health, meaning people with preexisting asthma and COPD are at risk for exacerbations, and probably for respiratory tract infections as well.” He said, “It’s a little less clear, but there’s good biological plausibility for increased risk of respiratory tract infections because when your alveolar macrophages are overloaded with carbon particles that are toxic to those cells, they don’t function as well as a first line of defense against bacterial infection, for example.”
The new normal of wildfires
Warmer, drier summers in recent years in the western United States and many other regions, attributed by climate experts to global climate change, have produced catastrophic wildfires (PNAS;2016 Oct 18;113[42]11770-5; Science 2006 Aug 18;313:940-3). The Camp Fire in Northern California broke out in November 2018, took the lives of at least 85 people, and cost more than $16 billion in damage. Smoke from that blaze reached hazardous levels in San Francisco, Sacramento, Fresno, and many other smaller towns. Other forest fires in that year caused heavy smoke conditions in Portland, Seattle, Vancouver, and Anchorage. Such events are expected to be repeated often in the coming years (Int J Environ Res Public Health. 2019 Jul 6;16[13]).
Wildfire smoke can contain a wide range of substances, chemicals, and gases with known and unknown cardiorespiratory implications. “Smoke is composed primarily of carbon dioxide, water vapor, carbon monoxide, particulate matter, hydrocarbons and other organic chemicals, nitrogen oxides, trace minerals and several thousand other compounds,” according to the U.S. Environmental Protection Agency (Wildfire smoke: A guide for public health officials 2019. Washington, D.C.: EPA, 2019). The EPA report noted, “Particles with diameters less than 10 mcm (particulate matter, or PM10) can be inhaled into the lungs and affect the lungs, heart, and blood vessels. The smallest particles, those less than 2.5 mcm in diameter (PM2.5), are the greatest risk to public health because they can reach deep into the lungs and may even make it into the bloodstream.”
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.
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).
Long-term effects unknown
When it comes to the long-term effects of wildfire smoke on human health outcomes, much less is known. In a recent literature review, Colleen E. Reid, PhD, and Melissa May Maestas, PhD, found only one study that investigated long-term respiratory health impacts of wildfire smoke, and only a few studies that have estimated future health impacts of wildfires under likely climate change scenarios (Curr Opin Pulm Med. 2019 Mar;25:179-87).
“We know that there are immediate respiratory health effects from wildfire smoke,” said Dr. Reid of the department of geography at the University of Colorado Boulder. “What’s less known is everything else. That’s challenging, because people want to know about the long-term health effects.”
Evidence from the scientific literature suggests that exposure to air pollution adversely affects cardiovascular health, but whether exposure to wildfire smoke confers a similar risk is less clear. “Until just a few years ago we haven’t been able to study wildfire exposure measures on a large scale,” said EPA scientist Ana G. Rappold, PhD, a statistician there in the environmental public health division of the National Health and Environmental Effects Research Laboratory. “It’s also hard to predict wildfires, so it’s hard to plan for an epidemiologic study if you don’t know where they’re going to occur.”
Dr. Rappold and colleagues examined cardiopulmonary hospitalizations among adults aged 65 years and older in 692 U.S. counties within 200 km of 123 large wildfires during 2008-2010 (Environ Health Perspect. 2019;127[3]:37006. doi: 10.1289/EHP3860). They observed that an increased risk of PM2.5-related cardiopulmonary hospitalizations was similar on smoke and nonsmoke days across multiple lags and exposure metrics, while risk for asthma-related hospitalizations was higher during smoke days. “One hypothesis is that this was an older study population, so naturally if you’re inhaling smoke, the first organ that’s impacted in an older population is the lungs,” Dr. Rappold said. “If you go to the hospital for asthma, wheezing, or bronchitis, you are taken out of the risk pool for cardiovascular and other diseases. That could explain why in other studies we don’t see a clear cardiovascular signal as we have for air pollution studies in general. Another aspect to this study is, the exposure metric was PM2.5, but smoke contains many other components, particularly gases, which are respiratory irritants. It could be that this triggers a higher risk for respiratory [effects] than regular episodes of high PM2.5 exposure, just because of the additional gases that people are exposed to.”
Another complicating factor is the paucity of data about solutions to long-term exposure to wildfire smoke. “If you’re impacted by high-exposure levels for 60 days, that is not something we have experienced before,” Dr. Rappold noted. “What are the solutions for that community? What works? Can we show that by implementing community-level resilience plans with HEPA [high-efficiency particulate air] filters or other interventions, do the overall outcomes improve? Doctors are the first ones to talk with their patients about their symptoms and about how to take care of their conditions. They can clearly make a difference in emphasizing reducing exposures in a way that fits their patients individually, either reducing the amount of time spent outside, the duration of exposure, and the level of exposure. Maybe change activities based on the intensity of exposure. Don’t go for a run outside when it’s smoky, because your ventilation rate is higher and you will breathe in more smoke. Become aware of those things.”
Advising vulnerable patients
While research in this field advances, the unforgiving wildfire season looms, assuring more destruction of property and threats to cardiorespiratory health. “There are a lot of questions that research will have an opportunity to address as we go forward, including the utility and the benefit of N95 masks, the utility of HEPA filters used in the house, and even with HVAC [heating, ventilation, and air conditioning] systems,” Dr. Cascio said. “Can we really clean up the indoor air well enough to protect us from wildfire smoke?”
The way he sees it, the time is ripe for clinicians and officials in public and private practice settings to refine how they distribute information to people living in areas affected by wildfire smoke. “We can’t force people do anything, but at least if they’re informed, then they understand they can make an informed decision about how they might want to affect what they do that would limit their exposure,” he said. “As a patient, my health care system sends text and email messages to me. So, why couldn’t the hospital send out a text message or an email to all of the patients with COPD, coronary disease, and heart failure when an area is impacted by smoke, saying, ‘Check your air quality and take action if air quality is poor?’ Physicians don’t have time to do this kind of education in the office for all of their patients. I know that from experience. But if one were to only focus on those at highest risk, and encourage them to follow our guidelines, which might include doing HEPA filter treatment in the home, we probably would reduce the number of clinical events in a cost-effective way.”
The 2019 wildfire season is underway in many locales across the United States, exposing millions of individuals to smoky conditions that will have health consequences ranging from stinging eyes to scratchy throats to a trip to the ED for asthma or chronic obstructive pulmonary disease (COPD) exacerbation. Questions about long-term health impacts are on the minds of many, including physicians and their patients who live with cardiorespiratory conditions.
John R. Balmes, MD, a pulmonologist at the University of California, San Francisco, and an expert on the respiratory and cardiovascular effects of air pollutants, suggested that the best available published literature points to “pretty strong evidence for acute effects of wildfire smoke on respiratory health, meaning people with preexisting asthma and COPD are at risk for exacerbations, and probably for respiratory tract infections as well.” He said, “It’s a little less clear, but there’s good biological plausibility for increased risk of respiratory tract infections because when your alveolar macrophages are overloaded with carbon particles that are toxic to those cells, they don’t function as well as a first line of defense against bacterial infection, for example.”
The new normal of wildfires
Warmer, drier summers in recent years in the western United States and many other regions, attributed by climate experts to global climate change, have produced catastrophic wildfires (PNAS;2016 Oct 18;113[42]11770-5; Science 2006 Aug 18;313:940-3). The Camp Fire in Northern California broke out in November 2018, took the lives of at least 85 people, and cost more than $16 billion in damage. Smoke from that blaze reached hazardous levels in San Francisco, Sacramento, Fresno, and many other smaller towns. Other forest fires in that year caused heavy smoke conditions in Portland, Seattle, Vancouver, and Anchorage. Such events are expected to be repeated often in the coming years (Int J Environ Res Public Health. 2019 Jul 6;16[13]).
Wildfire smoke can contain a wide range of substances, chemicals, and gases with known and unknown cardiorespiratory implications. “Smoke is composed primarily of carbon dioxide, water vapor, carbon monoxide, particulate matter, hydrocarbons and other organic chemicals, nitrogen oxides, trace minerals and several thousand other compounds,” according to the U.S. Environmental Protection Agency (Wildfire smoke: A guide for public health officials 2019. Washington, D.C.: EPA, 2019). The EPA report noted, “Particles with diameters less than 10 mcm (particulate matter, or PM10) can be inhaled into the lungs and affect the lungs, heart, and blood vessels. The smallest particles, those less than 2.5 mcm in diameter (PM2.5), are the greatest risk to public health because they can reach deep into the lungs and may even make it into the bloodstream.”
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.
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).
Long-term effects unknown
When it comes to the long-term effects of wildfire smoke on human health outcomes, much less is known. In a recent literature review, Colleen E. Reid, PhD, and Melissa May Maestas, PhD, found only one study that investigated long-term respiratory health impacts of wildfire smoke, and only a few studies that have estimated future health impacts of wildfires under likely climate change scenarios (Curr Opin Pulm Med. 2019 Mar;25:179-87).
“We know that there are immediate respiratory health effects from wildfire smoke,” said Dr. Reid of the department of geography at the University of Colorado Boulder. “What’s less known is everything else. That’s challenging, because people want to know about the long-term health effects.”
Evidence from the scientific literature suggests that exposure to air pollution adversely affects cardiovascular health, but whether exposure to wildfire smoke confers a similar risk is less clear. “Until just a few years ago we haven’t been able to study wildfire exposure measures on a large scale,” said EPA scientist Ana G. Rappold, PhD, a statistician there in the environmental public health division of the National Health and Environmental Effects Research Laboratory. “It’s also hard to predict wildfires, so it’s hard to plan for an epidemiologic study if you don’t know where they’re going to occur.”
Dr. Rappold and colleagues examined cardiopulmonary hospitalizations among adults aged 65 years and older in 692 U.S. counties within 200 km of 123 large wildfires during 2008-2010 (Environ Health Perspect. 2019;127[3]:37006. doi: 10.1289/EHP3860). They observed that an increased risk of PM2.5-related cardiopulmonary hospitalizations was similar on smoke and nonsmoke days across multiple lags and exposure metrics, while risk for asthma-related hospitalizations was higher during smoke days. “One hypothesis is that this was an older study population, so naturally if you’re inhaling smoke, the first organ that’s impacted in an older population is the lungs,” Dr. Rappold said. “If you go to the hospital for asthma, wheezing, or bronchitis, you are taken out of the risk pool for cardiovascular and other diseases. That could explain why in other studies we don’t see a clear cardiovascular signal as we have for air pollution studies in general. Another aspect to this study is, the exposure metric was PM2.5, but smoke contains many other components, particularly gases, which are respiratory irritants. It could be that this triggers a higher risk for respiratory [effects] than regular episodes of high PM2.5 exposure, just because of the additional gases that people are exposed to.”
Another complicating factor is the paucity of data about solutions to long-term exposure to wildfire smoke. “If you’re impacted by high-exposure levels for 60 days, that is not something we have experienced before,” Dr. Rappold noted. “What are the solutions for that community? What works? Can we show that by implementing community-level resilience plans with HEPA [high-efficiency particulate air] filters or other interventions, do the overall outcomes improve? Doctors are the first ones to talk with their patients about their symptoms and about how to take care of their conditions. They can clearly make a difference in emphasizing reducing exposures in a way that fits their patients individually, either reducing the amount of time spent outside, the duration of exposure, and the level of exposure. Maybe change activities based on the intensity of exposure. Don’t go for a run outside when it’s smoky, because your ventilation rate is higher and you will breathe in more smoke. Become aware of those things.”
Advising vulnerable patients
While research in this field advances, the unforgiving wildfire season looms, assuring more destruction of property and threats to cardiorespiratory health. “There are a lot of questions that research will have an opportunity to address as we go forward, including the utility and the benefit of N95 masks, the utility of HEPA filters used in the house, and even with HVAC [heating, ventilation, and air conditioning] systems,” Dr. Cascio said. “Can we really clean up the indoor air well enough to protect us from wildfire smoke?”
The way he sees it, the time is ripe for clinicians and officials in public and private practice settings to refine how they distribute information to people living in areas affected by wildfire smoke. “We can’t force people do anything, but at least if they’re informed, then they understand they can make an informed decision about how they might want to affect what they do that would limit their exposure,” he said. “As a patient, my health care system sends text and email messages to me. So, why couldn’t the hospital send out a text message or an email to all of the patients with COPD, coronary disease, and heart failure when an area is impacted by smoke, saying, ‘Check your air quality and take action if air quality is poor?’ Physicians don’t have time to do this kind of education in the office for all of their patients. I know that from experience. But if one were to only focus on those at highest risk, and encourage them to follow our guidelines, which might include doing HEPA filter treatment in the home, we probably would reduce the number of clinical events in a cost-effective way.”