Epidemiology

Asthma is currently a worldwide problem, with increasing prevalence in both children and adults. Total prevalence is estimated to be 7.2% of the world's population (6% in adults, 10% in children). There can be, however, wide variation between the prevalence of asthma in different countries and even within different areas of a country.

The most current and comprehensive epidemiologic data in the United States are collected by the National Center for Health Statistics (NCHS). This agency is an arm of the Centers for Disease Control (CDC). NCHS conducts a yearly survey of households called the National Health Interview Survey (NHIS). Among the questions asked are those that allow for the identification of persons with asthma.

The general prevalence of asthma in the United States is about 5%. In 1998, asthma affected an estimated 17.3 million persons in the United States, representing a 27% increase over 1993 [CDC, 1998]. Asthma tends to be a disease of young people. The prevalence of asthma is highest in children younger than age 18, and then it decreases with increasing age. However, the prevalence of asthma is rising in all age-groups, with the highest relative rise in preschool children (see figure below). The increase in children up to age 4 was about 160% from 1980-1994 [CDC, 1998].

Rising Prevalence of Asthma in the United States, 1980-1994

From Mannino et al. [1998]; with permission.
Click on image for larger version.

Gender also affects the prevalence of asthma, although this effect varies by age.

In children, the prevalence of asthma is higher in boys than girls. The male-to-female ratio of asthmatics is 3:2 among children ages 6-11 and increases to an 8:5 ratio among those ages 12-17.
In adults, and particularly among those ages 45-74, the gender ratio reverses. In these age-groups, asthma is more prevalent in women.

Another factor affecting the prevalence of asthma is race, although socioeconomic factors may also explain some of the racial differences. Of concern is the greater morbidity and mortality observed in African-American asthmatics compared with Caucasian asthmatics.

The prevalence of asthma is also impacted by socioeconomic and environmental factors. Environmental factors include exposure to aeroallergens (e.g., dust mites and cockroaches) or air pollution. Living in an inner city may expose an individual to greater levels of these factors. Data from the NHIS also show a greater prevalence of asthma in patients associated with lower income levels.

Links between heredity and asthma prevalence are important. The term atopy has special significance. Atopy refers to the inherited predisposition to allergic diseases such as asthma, allergic rhinitis, or eczema. Atopy underlies almost all asthma in children and most asthma in adults. The development of asthma in an atopic individual depends on exposure to specific allergens, infections, or other environmental influences.

Mortality

Asthma was not generally considered to be a fatal illness and this was the teaching in medical schools well into the present century. It was not until the rise in deaths from asthma in the 1960s that attitudes began to change.

The increasing death rate during the 1980s has been particularly alarming. As shown in the following figure, in the United States about 5500 asthmatics died across all age-groups in 1994. Deaths approximately doubled in each age range from 1980-1995 [CDC, 1998]. Mortality rates were consistently higher in blacks than in Caucasians, regardless of age, from 1980-1994.

Rising Asthma Deaths in the United States, 1980-1994

From Mannino et al. [1998]; with permission.
Click on image for larger version.

Morbidity

About 60% of all asthmatics in the United States visit their physician at least once a year regarding their condition. Office visits doubled from 1975-1994 [CDC, 1998] (see table below). Emergency department (ED) visits and hospitalizations are also increasing, with 466,000 hospitalizations in 1993 and 1.9 million ED visits in 1995.

Office (1980-1994) and ED Visits (1992-1995) and Hospitalizations (1980-1994) Due to Asthma

Office Visits ED Visits Hospitalizations

Age (years) 1994 Increase from 1980 (%) 1995 Increase from 1992* (%) 1994 Increase from 1980 (%)

0-4 1,024,000 98 248,000 -14 97,000 73

5-14 2,004,000 23 322,000 11 67,000 20

15-34 1,876,000 65 566,000 29 78,000 15

35-64 3,982,000 164 630,000 75 139,000 9

>65 1,488,000 119 101,000 13 85,000 8

Total 10,374,000 90 1,867,000 27 466,000 21

*Data unavailable for 1980.
From CDC [1998].

The effect asthma has on an individual's quality of life and the extent to which it may restrict daily activities is often overlooked. Yet, it is an important part of understanding this condition and the benefits that effective treatment can bring. Results from a 1998 survey conducted by the American Lung Association (ALA) highlight these quality-of-life issues.

Asthma significantly disrupts lives.

87% of parents and 84% of adult patients report that asthma has had a negative impact on their or their child's lives.
23% of adult patients and 36% of parents of asthmatics missed work during the past year because of their asthma (ALA survey).

Asthma is not under control.

83% of parents and 75% of adult patients reported unscheduled visits to the physician during 1998 because of asthma attacks.

Asthmatics adapt their lifestyle to accommodate their asthma. And they do not lead a "normal" life.

61% of all asthma patients and 73% of children report that they limit sports participation or exercise, find it difficult to sleep through the night, and make unplanned trips to the physician or ED.

Families, with members who have asthma, adapt to accommodate asthma and lack a "normal" family life.

70% of parents and patients agree that the whole family is affected by one member's asthma, and nearly 50% say asthma limits the range of activities the family can do together.

Many asthmatics do not know the difference between the controller medication that keeps symptoms from occurring and the reliever medication that can alleviate an attack.

73% of adult patients and 79% or parents of asthmatics actually named a reliever medication when asked to name a controller medication.

In children:

Asthma is the most common chronic illness and is the highest ranking chronic condition causing hospitalization [CDC, 1998].
Asthma is the primary chronic illness resulting in school absences (1998 ALA survey); asthmatic children have three times the school absences than those without the disease [Fowler et al., 1992].

Socioeconomics

The social and economic burdens associated with the increasing prevalence of asthma and related mortality make appropriate strategies for management extremely important. As shown in the figure below, the total direct and indirect cost estimates for asthma in 1994 amounted to $5.82 billion [Smith et al., 1997]. Direct costs were about 88% and indirect costs about 12% of the total. Hospitalizations represented the single greatest cost category, accounting for 54% of total direct costs at $2.80 billion. The next largest expenditure was for outpatient visits, accounting for 23% of total direct costs at $1.18 billion. Medication costs were lower, representing 16% of total direct costs at $817 million. ED visits were the smallest cost category at 7% of total direct costs at $348 million. For patients with asthma, indirect costs were incurred when the severity of the symptoms interfered with the patient's (or his family's) lifestyle. Thus, most indirect costs are associated with uncontrolled asthma.

Direct and Indirect Costs Associated with Asthma Care in the United States, 1994 dollars

Adapted from Smith et al. [1997]; with permission.
Click on image for larger version.

For children younger than age 17, the estimated total direct cost for asthma in 1994 was $1.63 billion [Smith et al., 1997]. Hospitalizations also represented the single greatest cost category in this age-group, accounting for 54% of total direct costs at $872 million. The next largest expenditure was outpatient visits at 21% of total direct costs at $340 million. Medication costs ranked as a lower expenditure at 14% of total direct costs at $235 million. ED visits were the smallest cost category at 11% of total direct costs at $182 million. The economic cost to caregivers — associated with 3.6 million school days missed and with preschoolers confined to bed — was $213 million.

Compared with children without asthma, children with the disease (age 1-17) incurred 2.8-fold higher total health care costs per year ($1129 vs $468) [Lozano et al., 1999]. Children with asthma needed 3.1-fold more prescriptions, made 2.2 -fold more visits to the ED, made 1.9-fold more nonurgent outpatient visits, and had 3.5-fold more hospitalizations.

Total direct costs for children up to age 4 ($792 million) are similar to that for those ages 5-17 ($839 million) [Smith et al., 1997]. As noted, hospitalizations account for the largest portion of direct costs of pediatric asthma. Hospital stays in these age-groups are also associated with increased indirect costs because caregivers take time off from work. However, there is disproportionate use of hospital care for children up to age 4 (74%) compared with those ages 5-17 (34%) [Smith et al., 1997]; see figure below. The disproportionate need for hospital care for preschool children may be due to misdiagnosis or undertreatment of asthma in this age-group. Also, physicians may hesitate to diagnose asthma in children. Alternatively, many children with the diagnosis of asthma are prescribed a beta-agonist, commonly without a controller therapy. Thus, a very young child with respiratory decompensation, especially if not assessed or treated appropriately, appears to require hospitalization more quickly than an older child.

Distribution of Direct Costs in Children by Age

Adapted from Smith et al. [1997]; with permission.
Click on image for larger version.

References

Centers for Disease Control. Forecasted state-specific estimates of self-reported asthma prevalence -- United States, 1998. MMWR Morb Mortal Wkly Rep. 1998;47:1022-1025.

Fowler MG, Davenport MG, Garg R. School functioning of US children with asthma. Pediatrics. 1992;90:939-944.

Lozano P, Sullivan SD, Smith DH, et al. The economic burden of asthma in US children: estimates from the National Medical Expenditure Survey. J Allergy Clin Immunol. 1999;104:957-963.

Mannino DM, Homa DM, Pertowski CA, et al. Surveillance for asthma -- United States, 1960-1995. Mor Mortal Wkly Rep CDC Surveill Summ. 1998;47:1-27.

Smith DH, Malone DC, Lawson KA, et al. A national estimate of the economic costs of asthma. Am J Respir Crit Care Med. 1997;156(3 Pt 1):787-793.

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