What are the incidence and prevalence of asthma?  
i.e. How many new cases of asthma are there per year now?  In recent
past years?  How many people have asthma in the U.S. now? In recent
past years?
Thanks!

Hi doctorway-ga, and thanks for your question.

The best source for the most recent information on asthma is the CDC
and the National Center for Health Statistics.  Here is the main CDC /
NCHS page for Asthma:

http://www.cdc.gov/nchs/fastats/asthma.htm

More detailed statistics are available from the Summary Health
Statistics for US Adults from 2003:
http://www.cdc.gov/nchs/data/series/sr_10/sr10_225.pdf

=========
Prevalence:
=========

According to this document, for adults (over 18), "[t]en percent had
ever been told they had asthma, and 6% still had asthma."  [p. 13]

Table 3 on pages 20-21 (pages 28-29 of the PDF) contains a detailed
breakdown of asthma prevalence within various age, race, education,
socioeconomic class, and other subgroups.  Table 4 (pages 30-31) gives
the same information expressed as percentages.

______________

For children (under 18), the following CDC document contains similar
data to that presented above for 2004:

"Nine million U.S. children under 18 years of age (12%) have ever been
diagnosed with asthma. As the age increases, the percentage of
children ever diagnosed with asthma increases."

Table I of this document (page 8; page 15 of the PDF) states that
12.2% of children ever had asthma (8,890,000).  This table also gives
data on number of children who had had an asthma attack over the prior
12 month period (5.5%).

This table also gives breakdowns for various subgroups and regions of the country.

There is additional data in Tables IV-V (Appendix III, page 55-56;
page 62-63 of the PDF).

You can find additional useful information and charts on asthma
prevalence (lifetime and current) in this document:

http://www.nlm.nih.gov/cgi/medlineplus/leavemedplus.pl?theURL=http%3A%2F%2Fwww%2Elungusa%2Eorg%2Fatf%2Fcf%2F%7B7A8D42C2%2DFCCA%2D4604%2D8ADE%2D7F5D5E762256%7D%2FASTHMA2%2EPDF

The above document also includes a map showing state-by-state prevelance.


Here is another summary document (only 2 pages) gives some numbers on
prevalence of asthma and it's effects from the US EPA:
http://www.nlm.nih.gov/cgi/medlineplus/leavemedplus.pl?theURL=http%3A%2F%2Fwww%2Eepa%2Egov%2Fiaq%2Fasthma%2Fpdfs%2Fasthma%5Ffact%5Fsheet%5Fen%2Epdf


You can find detailed (country-by-country) US data for asthma
prevalence within the American Lung Association document (free
registration is required):
http://www.kintera.org/autogen/home/default.asp?ievent=177849


========
Incidence:
========

Incidence is a little more tricky for a disease like asthma, where the
incidence (new cases) is low, but the prevalence (total ever cases) is
high.  I'll calculate this from the 2002 and 2003 data as follows:

There were a total of approximately 72,973,000 kids (under 18) in the
US in 2003 and 72,970,000 in 2002.  The number who were ever told they
had asthma in 2003 was 8,894,000 and in 2002 was 9,071,000.  This
means there were 177,000 new asthma cases between 2003 and 2002.  This
corresponds to an incidence rate of 177,000 / 72,970,000 * 1000 = 2.4
new cases per thousand children under 18.

======
Trends:
======

There have been some conflicting reports on asthma prevalence and
incidence trends.  For a review, I recommend this article:

von Hertzen L, Haahtela T.  Signs of reversing trends in prevalence of asthma.
Allergy. 2005 Mar;60(3):283-92. Review. 
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=abstract&list_uids=15679712&query_hl=8&itool=pubmed_docsum

The full text of this article (reprint) can be requested from Dr. von
Hertzen in Finland:
leena.vonhertzen@kolumbus.fi


This article also discusses asthma prevalence trends:
Guill MF. Asthma update: epidemiology and pathophysiology. Pediatr
Rev. 2004 Sep;25(9):299-305. Review.
http://www.ncbi.nlm.nih.gov.ezproxy.umassmed.edu/entrez/query.fcgi?cmd=retrieve&db=pubmed&list_uids=15342820&dopt=Abstract

You can request a reprint from Dr. Guill at the Medical College of Georgia:
MGUILL@MCG.EDU

Figure 1 of the above article gives the trends for prevalence back to
1980.  You can view this figure here:
http://img49.imageshack.us/img49/8102/fig10gz.jpg

http://www.cdc.gov/mmwr/preview/mmwrhtml/ss5101a1.htm

===================

I hope this information is useful.  Please feel free to request
clarification prior to rating.

     -welte-ga

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Request for Answer Clarification by doctorway-ga on 26 Jun 2006 07:52 PDT

This is great!  Are there any reference sources for incidence, though,
or example numbers, outside of calculation?  I've heard vastly
different anecdotal incidence rates from 1% up to 17% -- not sure what
to believe.

---

Clarification of Answer by welte-ga on 28 Jun 2006 08:45 PDT

Hi doctorway-ga,

Sorry for the delay in getting back to you - the clarification
notification system has been down for a while apparently.

I was unable to find hard, reliable numbers for incidence ro incidence
rates that were any more recent than about 1998, which is why I went
with calculation.  The numbers I gave are likely the most accurate
available, since they are based on the national disease database
numbers, which tracks the number of cases each year more thoroughly
than any other source.  I think that incidence in asthma is not
discussed much in research articles or online sources because asthma
is a chronic, lifelong problem, with a small incidence but a much
larger prevalence (relatively few new cases per year, but a large
cumulative number of people with the disease).

   -welte-ga