Slide 4: Epidemiology
Epidemiology is the study of the distribution and determinants of
diseases and injuries in human populations. Epidemiologists describe who
has a disease in a population to help identify its causes. Once the
cause is understood, interventions can be developed to prevent, manage,
and control the disease.
Although much is known about asthma physiology, triggers, and treatment,
more information is needed to adequately define the scope of the problem
across the country and to help pinpoint the actual cause of the disease.
Epidemiologic studies will help us better understand which
subpopulations are most severely affected by asthma and why. That
information can help us focus interventions where they can be the most
effective.
Slide 5: Asthma Prevalence by Age, U.S.,
1980-1996
Historically, the prevalence of asthma has been measured from a question
on the National Health Interview Survey. It is simply the percentage of
respondents who answer "yes" to the question "In the past 12 months, has
anyone in the family had asthma"? This slide demonstrates the increase
in 12-month asthma prevalence from 1980 to 1996. After 1996, the
question about asthma was changed to ask about lifetime, medically
diagnosed asthma. We can no longer measure asthma prevalence comparable
to the 12-month prevalence value.
In the graph, the yellow line indicates the percentage of the U.S.
population affected by asthma each year. The prevalence of asthma
increased from 3.1% in 1980 to 5.5% in 1996. The red and green lines
show the difference in the prevalence of asthma for children and adults.
The prevalence of asthma in children (under age 18 years) is higher than
it is in adults (age 18 and older). Asthma is the second most prevalent
chronic condition among children. It results in approximately 14 million
days of missed school each year. In 1980, 3.6% of children had asthma.
By 1995, the prevalence had increased to 7.5%, or approximately 5
million children. The decline to 6.2% for children in 1996 may be the
beginning of a new trend, or it may simply result from random variation
due to survey sampling procedures. In 1996, the sample size was
considerably smaller than it was in earlier years, which results in
greater variability in estimates.
Slide 6: Asthma Prevalence by Sex, U.S.,
1982-1996
This graph shows prevalence from 1982 to 1996 by sex. The green line is
for females and the red line is for males. Before 1992, prevalence
differed only slightly. After 1992, however, the percentages for women
were significantly higher than those for men.
Slide 7: Asthma Prevalence by Race,
U.S., 1982-1996
This graph shows the prevalence from 1982 to 1996 by race. The green
line is for whites and the red line is for blacks. Although prevalence
for blacks each year is generally higher than that for whites, it is
only significantly higher for 5 of the 15 years - 1988, 1991, 1993,
1995, and 1996. In 1996, the percentage for blacks was 7.0% and the
percentage for whites was 5.3%.
Slide 8: Asthma Prevalence by Race, Ages
5-34, U.S., 1980-1996
Some researchers believe that 5 to 34 is a better age range for studying
asthma because it is not confounded by the difficulty of diagnosis in
very young children and by other diseases in the older population. This
graph shows 12-month asthma prevalence for those age 5-34 by race.
Slide 9: Asthma Hospital Discharge Rates
by Sex, U.S., 1980-1998
One way we can assess the morbidity, or impact on quality of life, of a
particular illness is by determining the rate of hospitalizations from
that illness. From 1980 to 1998, rates were consistently higher for
females than for males. Asthma unnecessarily reduces the quality of life
for many people. For example, hospitalizations for asthma cause people
to miss school, work, and other activities. With proper disease
management, however, people with asthma can lead more healthy, active
lives.
Slide 12: Age-Adjusted Asthma Mortality
Rates by Sex, U.S., 1979-1998
During 1993 through 1998, more than 5,000 Americans died from asthma
each year. With proper asthma management, many of these deaths might
have been prevented. The green line is the mortality rate for women and
the red line is for men. The yellow line represents the total
population.
Clearly, asthma mortality rates rose during that period. Women have had
higher mortality rates than men since 1981, but they did not have higher
prevalence rates than men until after 1991. Most of the increase
occurred before 1992 and the increase was greater in women than it was
in men. Researchers have not yet determined the cause of the increase.
Slide 14: Asthma Mortality Rates by
Race, Ages 5-34, U.S., 1979-1998
The 5- to 34-year age category is often used because some studies have
shown that asthma is most accurately identified as a cause of death in
that age group. Even though the rates are lower than those for all ages
combined, asthma mortality rates clearly rose for this age group as
well. Rates for the white and other race categories did not differ for
this age group, and the rates for blacks were much higher.
Slide 15: Costs of Asthma
Kevin Weiss, et al. estimated that the cost of asthma in the United
States in 1990 was 6.2 billion dollars and in 1998 was 12.7 billion
dollars. Using figures from the later time, costs for 2000 would be
around 13.8 billion dollars. The direct costs of asthma include the
costs of asthma management programs, inpatient and outpatient medical
care, physician services, emergency visits, ambulance use, drugs,
short-term and long-term treatment complications, devices, nursing
services, allergy testing, and research. Some of the indirect costs of
asthma include absence from work and school; travel; time waiting for
care; and at its most extreme, death. Costs most difficult to measure
are anxiety, pain, suffering, and decreased potential resulting from
school absenteeism.
Asthma drains the nation's health-care budget. Time, energy, and money
are being spent in hospitals and emergency departments where services
are expensive and do not address long-term reduction of symptoms.
Although appropriate management of people with asthma should decrease
the overall cost of the disease to society, the most important benefit
would be the improved health and well being of people with asthma and
their families.
