Asthma FAQ
Q1. How many Americans have ever had asthma?
A1. The most recently available data is from the 2000 National Health
Interview Survey. Based on the proportion of respondents who answered
"yes" to the question: "Has a doctor or other health
professional ever told you that you had asthma?Ó it is estimated
that 27.6 million people have had a diagnosis of asthma in their lifetime.
This includes 8.9 million children under age 18 years. Lifetime asthma
diagnosis is not a useful measure of the current public health problem
of asthma because many people diagnosed with asthma earlier in life
may no longer suffer from it or may have it under control. Based on
the persons who also answered yes to the subsequent question: "During
the past 12 months have you had an episode of asthma or an asthma attack?"
an estimated 11 million people (of which 4 million are children) had
a recent asthma attack. This is a useful public health measure because
it provides an estimate of people with asthma who are at risk of poor
health outcomes and who use more health care resources. The persons
who answered "no" to the subsequent question represent 16.6
million people who (1) have resolved asthma or (2) have current but
well-managed asthma. Beginning in 2001, the prevalence of people with
current asthma but who have not had an attack in the past 12 months
is also being measured.
Q2. How many Americans currently have asthma?
A2. When the data from the 2001 National Health Interview Survey are
available, we will be able to answer this question about current asthma,
but at present we can only estimate the number of persons who have had
at least one attack of asthma in the past 12 months. The National Health
Interview Survey reported that an estimated 11 million persons experienced
at least one attack of asthma during 2000. This represents persons who
answered "yes" to the following two questions: "Has a
doctor or other health professional ever told you that you had asthma?"
and "During the past 12 months have you had an episode of asthma
or an asthma attack?" We call this estimate the "asthma attack
prevalence." Note that this is not the number of asthma attacks
in one year, as one person can have more than one attack, but it is
the number of individuals who reported at least one attack in the past
year. Beginning in 2001, the prevalence of both current asthma and asthma
attack are being measured.
Q3. Is asthma increasing or decreasing?
A3. During the period 1980 to 1996 the prevalence of asthma was determined
from the National Health Interview Survey question: "During the
past 12 months has anyone in the family had asthma?" The number
of persons in the United States reported to have asthma doubled between
1980 and 1996, from 7.0 million to 14.6 million persons.
In 1997 we changed the way we estimate the prevalence of asthma. Data
before and after 1996 cannot be directly compared. First, the asthma
questions changed in 1997 to measure prevalence of lifetime asthma diagnosis
and asthma attack prevalence. Second, the 1997 survey design was changed
to make the data more reliable. Since 1997, asthma data are gathered
for the whole NHIS sample rather than one-sixth of the sample as was
done pre-1997; also, second-hand or ÒproxyÓ reporting
for other household members was phased out except for children. For
the four years between 1997 and 2000, which can be compared to each
other, there is no evidence of an increase in prevalence of lifetime
asthma diagnosis or asthma attack prevalence.
In summary, asthma prevalence increased from 1980 to 1996, but more
data are needed to establish a new and reliable trend after 1997. Asthma
attack and lifetime asthma diagnosis prevalence remained relatively
stable from 1997 to 2000.
Q4. Why has asthma prevalence increased from 1980 to 1996?
A4. There have been many theories put forward to explain the increase
between 1980 and 1996, but in general, the reasons behind rising asthma
prevalence, hospitalizations, and death rates are not well understood.
It is likely that many factors are responsible, and current theories
include: exposures to allergens, pollutants and infections; obesity,
diet and physical activity; awareness and reporting of asthma by health
care workers and the public; and use of antibiotics. Just as it is poorly
understood why asthma increased from 1980 to 1996, it is also not well
understood why asthma attack prevalence and lifetime asthma diagnosis
have remained steady from 1997 to 2000.
Q5. How many new cases of asthma occur each year in the United States?
A5. Because asthma is an intermittent chronic disease that does not
require reporting to health authorities, estimates of "new cases"
are not available. We can address the question indirectly by noting
that the number of persons estimated to have the disease was 7.5 million
more in 1996 than in 1980, an average increase of over 450,000 persons
per year, but not all of these are new cases.
Q6. Why were the NHIS questions changed?
A6. The survey was redesigned in 1997 to increase the reliability of
the estimates, reduce the length of the interviews, and focus on the
most important public health problems. There was also a need to incorporate
ongoing methodical advances in the measurement of asthma and to increase
comparability across surveys. An important part of the redesign was
to eliminate "second-hand," or "proxy" reports from
one household member for other adults in the household, as these can
be inaccurate. Proxy reports are still used for children. To further
improve estimates, respondents are now asked whether they were ever
told by a doctor or other health care professional that they had asthma.
It was also important to determine if the asthma had been active recently
by asking whether the person had experienced an attack in the past 12
months.
Q7. What has been the impact of the change in questions-- are current
estimates better or worse than past estimates?
A7. The new estimates are believed to be better than past estimates,
though they have the disadvantage of not being comparable to earlier
data. The survey question asked before 1997 was: "During the past
12 months did anyone in the family have asthma?" This question
did not require a diagnosis by a health professional. It included "second-hand"
or "proxy" responding for adults not in the house at the time
of the survey. In addition, since the entire NHIS sample is asked about
asthma in the redesigned survey (compared to about one-sixth of the
sample before the redesign), the prevalence estimates after 1997 are
more precise. From 1997-2000, the NHIS includes an initial screening
question to determine who in their lifetimes were told by a doctor or
other health professional that they had asthma (27.6 million in 2000).
It then follows up the first question by identifying those who had an
attack or episode of asthma in the past 12 months (11 million in 2000).
Beginning in 2001, the prevalence of people with current asthma but
who have not had an attack in the past 12 months is also being measured.
