Which Groups of Children Are Most Impacted by Childhood Asthma?
Asthma has been found in children of all ages, of both genders, and in all ethnicities; however, the prevalence of asthma varies throughout life and to varying degrees between gender and ethnicities. Socioeconomic factors are also important, and asthma remains a disease that reflects larger health disparities in the United States. The most common risk factors for asthma continue to involve the complex interplay between familial and genetic influences coupled with infectious and noninfectious environmental exposures at critical developmental periods. Cases of asthma tend to be grouped in families that have a high incidence of atopy, and asthma is common in certain ethnic groups and among socially disadvantaged members of society (see Question 2).
Children may develop asthma at different ages of their life, but the prevalence of asthma tends to increase with age. The overall prevalence of asthma in children 0 to 4 years of age was 6.2% in 2005. This increased to an overall prevalence of 9.3% in children 5 to 10 years of age. Finally, there was a small but continued increase to 10.0% in those children ages 11 to 17 years. This results in an overall prevalence of 9.6% asthma in children younger than age 18. This trend is in contrast to medical resource utilization including outpatient visits, emergency room visits, and hospitalizations, which tend to decrease as children with asthma get older. Thus, despite the lowest prevalence of asthma at the youngest ages (younger than 2 years), there tends to be the highest medical resource utilization (Figure 3-1) among children in this age group.
Figure 3-1. The proportional impact of asthma prevalence, health care use, and mortality among children 0 to 17 years of age, by age group, United States, 2003–2005. (Adapted from data from the Centers for Disease Control/National Center for Health Statistics, National Health Interview Survey, National Hospital Ambulatory Medical Care Survey, and the Mortality Component of the National Vital Statistic System.)
This inverse relationship of asthma prevalence and medical resource utilization is thought to be multifactorial. There is difficulty differentiating airway inflammation and symptoms due to asthma from airway inflammation due to recurrent viral infections at young ages, and this may delay a formal diagnosis of asthma. However, the tendency of the small airways of young children to become obstructed may result in much more dramatic and severe symptoms during asthma flares that warrant increased urgent medical care. Similarly, viral infections are more frequent in young children. As children get older, there is greater confidence in eliciting a history of chronic coughing and wheezing associated with common asthma triggers. There may also be a greater self-awareness of symptoms and enhanced ability to identify asthma flares earlier in their course that may preclude the need for urgent evaluations. On the other hand, adolescents remain a medically underserved population and are notorious for denying, under-reporting, or misperceiving asthma symptoms.
There is a discrepancy between males and females and the impact of asthma in most age groups in childhood. The prevalence and medical resource utilization is slightly higher in boys than in girls from infancy through adolescence. The most recent data from the Centers for Disease Control (CDC) report that the overall asthma prevalence in boys is 11.3%. However, in late adolescence (15 to 17 years of age), the prevalence of asthma in girls (10.5%) exceeds boys (10.1%), and this trend continues into adulthood. There is also a greater use of medical resources in the ambulatory setting by teenage girls than boys, although hospitalization and death rates remain slightly higher in boys. This inverse relationship between utilization of medical resources in the ambulatory setting and asthma-related hospitalization or death is also seen in the racial disparity of asthma.
The impact of race and ethnicity is a complex and fluid interaction of genetics and environment. Prevalence rates of asthma range from the lowest in children of Asian descent to the highest in those children of Puerto Rican ethnicity (Table 3-1). Non-Hispanic Black children also have a strikingly high asthma prevalence of 17% according to the most recently published statistics from the CDC. Table 3-1 also shows the inverse relationship between the number of ambulatory visits and the number of deaths. Non-Hispanic Black children have the lowest number of ambulatory visits and the highest number of deaths, but non-Hispanic White children have the highest number of ambulatory visits and the lowest number of deaths. This suggests a strong influence from social and environmental factors and indicates potential barriers to seeking appropriate outpatient care to establish asthma control rather than simply a genetic predisposition toward more brittle or severe asthma.
As the previously cited trends and statistics suggest, social, economic, racial, and gender-related factors are critical to asthma prevalence and severity. This is also reflected in the frequency and severity of what has been termed inner-city asthma. In the past several decades, it has become apparent that the burden of asthma has grown disproportionately among children residing in urban areas and particularly the inner cities of the United States. A multitude of factors are thought to contribute to this explosion of asthma among inner city children, many of whom are poor, socially and medically disadvantaged, and members of ethnic minority groups (Table 3-2). Factors such as poor living conditions, high levels of air pollution, the components of which can be immunomodifying and impact lung growth, and unique indoor allergens (eg, cockroach antigen) all contribute. Other factors, such as suboptimal access to medical care and inadequate care delivery, are important as well.
Air pollution can have a major impact on children’s respiratory health in many ways that are relevant to asthma. Air pollution is composed of many things, but particulate matter, nitrogen oxides, and ozone are most important to asthma and children’s respiratory health. Levels of air pollution derived from the burning of fossil fuels can impact lung growth and function. Studies in Los Angeles have shown clear relationships between exposure to air pollution and levels of lung function in children. The closer a child lives to one of Los Angeles’ famous freeways, the lower the level of his or her lung function. The individual components of air pollution can be toxic to the lung as well. Diesel exhaust particles have been shown to promote airway inflammation and modify the immune responses of airway epithelial cells, and truck traffic is an enormous contributor to toxic air pollution. Other components of smog, such as ozone, also cause lung inflammation.
Studies have shown clear relationships between levels of air pollution and asthma episodes in children. During the 1996 summer Olympic Games in Atlanta, the limitation of driving into the city during the games resulted in reduced air pollution that was clearly linked to reduced asthma morbidity in children. From these studies and others, it is clear that the quality of the air we breathe has important effects on children’s respiratory health and asthma burden. While cause and effect are always very difficult to prove, perhaps it is not too surprising that asthma has begun to concentrate in urban areas that are sites of poor indoor, as well as outdoor, air quality. An important public health goal that has high relevance to asthma is to support legislation to minimize air pollution.
Currently in the United States, there is an asthma epidemic, with an unacceptably high prevalence of this disease among children during the past decades. This epidemic is not equally distributed, and the disproportionate burden of asthma borne by children residing in the inner cities and those of ethnic minority status is something that all clinicians should work to improve. Simply put, the differences in the impact of asthma vary by race, gender, and age. These differences place non-Hispanic Black teenage boys in the highest risk group of dying from asthma. They also emphasize the need to establish routine care in the ambulatory settings (especially in this group) because the number of ambulatory visits is inversely related to the number of deaths from asthma. Working to overcome barriers so that asthma care is equally accessible to all children is also an important goal. In the final analysis, all of us as pediatric providers will be treating a lot of children of all ages, races, and genders with asthma.
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