Certain lifestages and populations may be at greater risk of experiencing a health effect due to wildfire smoke and may experience more severe effects. These groups are referred to as at-risk populations. The Air Quality Index uses the term “sensitive groups.” Key risk factors that shape whether a population or individual is at greater risk of health effects from wildfire smoke have been identified primarily from epidemiologic studies examining exposure to fine particle pollution in urban settings.

Evidence indicates that the risk of fine particle-related health effects varies throughout a lifetime. Risk is generally higher during childhood, lower in young adulthood, and greater in middle age through old age as the incidence of heart and lung disease, hypertension, and diabetes increases. Therefore, certain lifestages (e.g., children, older adults) and populations (e.g., people with pre-existing respiratory and cardiovascular disease) should be particularly diligent about limiting exposure to wildfire smoke. All of your patients, but especially your patients who are members of these at-risk populations, should check the Air Quality Index (AQI) forecasts and current air quality each day during a smoke event and follow recommendations to reduce exposure:

• People with asthma and other respiratory diseases
• People with cardiovascular disease
• Children (< 18 years of age)
• Pregnant women
• Older adults
• People of low socio-economic status
• Outdoor workers

People with asthma and other respiratory diseases. More than 25 million people in the United States, including more than 6 million children, experience chronic lung diseases such as asthma, with another 16 million experiencing chronic obstructive pulmonary disease (COPD)(CDC 2017, CDC 2018).; Air pollution, such as wildfire smoke, may not affect healthy people, but for people with chronic lung diseases, such as asthma and COPD, it can lead to breathing difficulties and trigger exacerbations of their disease. Extensive evidence from epidemiologic studies focusing on exposure to fine particles demonstrates increased emergency department visits and hospital admissions related to exacerbations of asthma and COPD.

People with cardiovascular disease. Cardiovascular diseases are the leading cause of mortality in the United States, comprising approximately 30 to 40 percent of all deaths each year (Xu et al. 2018). Most of these deaths occur in people over 65 years of age. Diseases of the circulatory system (e.g., high blood pressure, heart failure, vascular diseases such as coronary artery disease, and cerebrovascular conditions) can put individuals at increased risk of cardiovascular-related events triggered by air pollutants.

• palpitations, unusual fatigue,
• lightheadedness,
• shortness of breath,
• chest tightness,
• pain in the chest neck, or shoulder.

Studies have linked fine particle pollution to increased risks of heart attacks, and sudden death from cardiac arrhythmia, heart failure, or stroke (U.S. EPA, 2009). Despite the evidence indicating a relationship between fine particle pollution and cardiovascular effects, wildfire-related cardiovascular studies have been inconsistent, although some more recent studies have identified elevated risks (e.g., Wettstein et al. 2018 [See Figure 2}, Deflorio-Barker et al. 2019).

Children (< 18 years of age). All children, even those with no pre-existing illness or chronic conditions, are considered sensitive to air pollution, including wildfire smoke. Compared to adults, children spend more time outside, tend to engage in more vigorous activity, and inhale more air (and therefore more smoke) per pound of body weight — all of which can affect the developing lungs (Sacks et al. 2011). For these reasons, it is important to try to limit children’s vigorous outdoor activities during wildfire events.

Symptoms of wildfire smoke inhalation, which can include coughing, wheezing, difficulty breathing, and chest tightness, are supported by evidence from epidemiologic studies of particulate matter that report increased respiratory symptoms and decreased lung function (U.S. EPA, 2009). Air pollution from wildfires can exacerbate asthma symptoms and trigger asthma attacks. Research has shown a higher rate of asthma emergency department visits and hospital admissions for children, especially infants and very young children, during and following wildfire events (Hutchinson et al., 2007). Even children who do not have asthma could also experience these symptoms, resulting in school absences and other limitations of normal childhood activities.

Children may also experience significant emotional distress resulting from anxiety and grief following a wildfire. It is important to consider not only the potential physical health implications of wildfire smoke on children, but also the potential longer-term psychological implications.

Pregnant women. During pregnancy, physiologic changes, such as higher respiratory rates and increases in blood and plasma volumes, increases a woman’s vulnerability to environmental exposures. Additionally, during critical windows of human development, a mother’s exposure to wildfire smoke may harm the developing fetus.

A few studies have examined potential health effects of wildfire smoke exposure during pregnancy, providing some evidence of impacts on birth outcomes (e.g., reduced birth weight), and that psychosocial stress from the wildfire event itself could affect the developing fetus (Kumagai et al. 2004; Holstius et al. 2012). While there are few studies examining the health effects of exposure to wildfire smoke on pregnancy outcomes, there is some available evidence of health effects due to exposures to other combustion-related air pollutants (e.g., cigarette smoke, indoor biomass smoke). Additionally, a large but inconsistent body of evidence on the health effects of prenatal exposure to ambient air pollution, specifically particle pollution, provides some evidence of higher rates of adverse birth and obstetrical outcomes (e.g., decreased infant birth weight, preterm birth) in response to chronic maternal exposure to particle pollution (U.S. EPA 2009).

Older adults. The number of U.S. adults 65 years of age and older will nearly double between 2012 and 2050 (Ortman et al. 2014). Older adults are at increased risk of health effects from short-term exposures to wildfire smoke because of their higher prevalence of pre-existing lung and heart diseases, and because important physiologic processes, including defense mechanisms, decline with age. Epidemiologic studies have reported greater risks of emergency department visits, hospital admissions, and mortality associated with short-term exposures to fine particle pollution in older adults (U.S. EPA, 2009).

People of low socio-economic status. Socio-economic status is often defined in epidemiologic studies using indicators such as educational attainment, median household income, percentage of the population in poverty, race/ethnicity, and location of residence. Socio-economic status is a composite measure that encompasses multiple characteristics and is often measured at the population- or community-level. Epidemiologic studies of fine particle pollution using indicators of socio-economic status provide initial evidence that in populations of low socio-economic status there may be an increased risk of mortality due to short-term exposures (U.S. EPA, 2009). With respect to wildfire smoke, the evidence is much more limited, although Rappold et al. (2012) and Reid et al. (2016) reported some evidence that locations classified as having the lowest socio-economic status were at the greater risk of health effects attributed to wildfire smoke.

In addition, socio-economic status may contribute to differential exposures to wildfire smoke across communities. For example, access to air conditioning reduces infiltration of particle pollution indoors. Less access to air conditioning may lead to greater exposure to wildfire smoke, increased sensitivity to extreme heat and, as a result, health disparities across communities. People of color and impoverished children and adults bear a disproportionate burden of asthma and other respiratory diseases and therefore they may be at increased risk of health effects from wildfire smoke exposure (Brim et al. 2008, CDC 2014). As a result, additional outreach activities and support may be required to properly communicate actions that people of low socio-economic status should take to reduce exposure to and protect themselves from wildfire smoke.

Outdoor Workers. Working outdoors during periods of wildfire smoke could result in a range of health effects depending on the underlying health status of the worker. Effects of exposure to wildfire smoke range from eye and respiratory tract irritation to the triggering of an asthma exacerbation or cardiovascular event.

Table 1. Summary of lifestages and populations potentially at greater risk of health effects due to wildfire smoke exposures.

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