Asthma has been known since antiquity, yet it is a disease that still defies precise definition. The word asthma is of Greek origin and means “panting.” More than 2000 years ago, Hippocrates used the word asthma to describe episodic shortness of breath; however, the first detailed clinical description of the asthmatic patient was made by Aretaeus in the second century.1 An expert panel of the National Institutes of Health, the National Asthma Education and Prevention Program (NAEPP), has provided the following working definition of asthma2:
Asthma is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role, in particular, mast cells, eosinophils, T-lymphocytes, macrophages, neutrophils, and epithelial cells. In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning.
These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. The inflammation also causes an associated increase in the existing bronchial hyperresponsiveness to a variety of stimuli.This definition encompasses the important heterogeneity of the clinical presentation of asthma by describing the scientific and clinically accepted characteristics of asthma.
EPIDEMIOLOGY
An estimated 14 to 15 million persons in the United States have asthma (about 5% of the population).Asthma is the most common chronic disease among children in the United States, with approximately 5 million children affected. Over the past two decades in the United States, the prevalence of asthma has increased by 75%, whereas the rate in children younger than age 5 has increased 160%.In the United States, as in other Western industrialized countries,the prevalence of asthma has reached epidemic proportions. Asthma accounts for 1.6% of all ambulatory care visits (13.7 million) and results in more than 470,000 hospitalizations and 2 million emergency department visits per year.3 Asthma is the third leading cause of preventable hospitalization in the United States, and hospitalizations for asthma among children 0 to 17 years of age have increased 4.5% per year, whereas total hospitalizations for all causes in children actually decreased. Children have the highest prevalence of asthma, at 68.6 per 1000 population younger than 18 years of age.
Asthma accounts for more than 10 million missed school days per year. The prevalence of disabling asthma in children has increased 232% over the past 20 years compared with a 113% increase from all other chronic conditions in childhood. In young children (0 to 10 years of age), the risk of asthma is greater in boys than in girls, becomes about equal during puberty, and then is greater in women than in men.3Ethnic minorities continue to share the burden of asthma disproportionately.
African-Americans and Hispanics have a higher prevalence than whites, but this appears to be a result of urbanization and not race or socioeconomic status. African-Americans are three times as likely to be hospitalized and approximately 2.5 times more likely to die from asthma.3 In addition, African-Americans and Puerto Ricans living in inner cities are four times more likely to experience emergency department visits than whites. These patterns are likely a result of poor access to care.
The estimated cost of asthma in the United States in 1998 was $12.6 billion.The average societal burden of asthma (including both direct and indirect medical expenditures) in the United States averages $640 per patient per year, with direct medical expenditures accounting for 40% to 50% of total costs. Emergency care of acute asthma exacerbations makes up the largest portion of direct medical costs. In 1997, an estimated cost of $1 billion dollars per year in lost productivity accrued from parents staying home to care for their children.
The natural history of asthma is still not well defined. Although asthma can occur at any time, it is principally a pediatric disease, with most patients being diagnosed by 5 years of age and up to 50% of children having symptoms by 2 years of age. Between 30% and 70% of children with asthma will improve markedly or become symptom-free by early adulthood; chronic disease persists in about 30% to 40% of patients, and generally 20% or less develop severe chronic disease. Atopic status is the strongest indicator of a poor prognosis, although initial severity also predicts severity as an adult.Diminished lung growth may occur in children with uncontrolled severeasthma. Lowlung function and increased bronchial hyperresponsiveness
are independent risk factors for low lung function in early
adulthood.In adults, most longitudinal studies have suggested a more rapid
rate of decline in lung function in asthmatics than in normal volunteers,
primarily reflected in forced expiratory volume in 1 second (FEV1). However, the annual decline in FEV1 is less than in smokers or in patients with a diagnosis of emphysema. In general, asthmatics with less frequent attacks and normal lung function on initial assessment have higher remission rates, whereas smokers have the lowest remission and highest relapse rates. The level of bronchial hyperresponsiveness (BHR) tends to predict the rate of decline in FEV1, with a greater decline with high levels of BHR. Thus airways obstruction in asthma not only may become irreversible but also may worsen over time owing to airway remodeling (see below).Although both the prevalence and the morbidity from asthma are increasing, the death rate from asthma in the United States appears to have reached a plateau of about 5000 deaths per year and may be on the decline.3 Despite the relatively low number of asthma deaths,80% to 90% are preventable.2 Most deaths from asthma occur outside the hospital, and death is rare after hospitalization. The most common cause of death from asthma is inadequate assessment of the severity of airways obstruction by the patient or physician and inadequate therapy. the most common cause of death in hospitalized patients is also inadequate or inappropriate therapy. Thus the key to preventio of death from asthma, as advocated by the NAEPP, is education.
