Correspondence
The Asthma Epidemic
N Engl J Med 2007; 356:1073March 8, 2007
- Article
To the Editor:
Eder and colleagues (Nov. 23 issue)1 describe the high prevalence and incidence of asthma in the Western world. However, survey instruments that rely on physicians' or patients' reports of diagnosis for case ascertainment do not provide robust measurements of asthma and may be unreliable for estimating its prevalence.2 No single instrument can identify asthma with certainty. Exacerbations of asthma are episodic, are of limited duration, and share clinical features with other disorders, complicating accurate diagnosis. In addition, no theory has been confirmed to explain an asthma epidemic.
The authors should comment more analytically on the possibility that asthma is overdiagnosed by clinicians3,4 and that social marketing may contribute to the increased diagnosis of asthma and, in turn, to the perception of an epidemic.5 Multicenter clinical trials of treatments for asthma that have well-defined enrollment criteria typically recruit few subjects as compared with trials of treatments for cardiovascular diseases with a similar reported prevalence. The reasons for this disparity defy simple explanation if the prevalence of asthma is 5.8% in the United States and is substantially higher in many other Western nations.1
5 ReferencesWare G. Kuschner, M.D.
Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304
ware.kuschnermd@va. gov 1
Eder W ,Ege MJ ,von Mutius E . The asthma epidemic. N Engl J Med 2006;355:2226-2235
Full Text | Web of Science | Medline2
Peat JK ,Toelle BG ,Marks GB ,Mellis CM . Continuing the debate about measuring asthma in population studies. Thorax 2001;56:406-411
CrossRef | Web of Science | Medline3
LindenSmith J ,Morrison D ,Deveau C ,Hernandez P . Overdiagnosis of asthma in the community. Can Respir J 2004;11:111-116
Medline4
Macy E ,Schatz M ,Gibbons C ,Zeiger R . The prevalence of reversible airflow obstruction and/or methacholine hyperreactivity in random adult asthma patients identified by administrative data. J Asthma 2005;42:213-220
Web of Science | Medline5
Barraclough R ,Devereux G ,Hendrick DJ ,Stenton SC . Apparent but not real increase in asthma prevalence during the 1990s. Eur Respir J 2002;20:826-833
CrossRef | Web of Science | Medline
Author/Editor Response
As we stated in our review article, the results of various epidemiologic studies suggest that “part of the increase in the prevalence of asthma is attributable to changes in diagnostic labeling. The magnitude of the resulting bias in different populations is, however, difficult to appraise.” Nevertheless, this bias is unlikely to completely explain the increase in the prevalence of asthma over time. First, there is evidence that the prevalence of objective markers associated with asthma, such as atopy, has increased over time, although these markers are admittedly not identical to asthma. Second, the bias will affect the rate of diagnosis of asthma by physicians in children with wheezing. In Aberdeen, Scotland, this rate has indeed increased: asthma was diagnosed in 28% of children with wheezing in 1964, in 49% of such children in 1989, and in 64% in 1999.1 Yet the prevalence of wheezing, not only the prevalence of the diagnosis of asthma by physicians, increased over time. Because most studies do not report the rate of diagnosed asthma among children with wheezing, the magnitude of the bias is difficult to appraise.
1 ReferencesWaltraud Eder, M.D.
Markus J. Ege, M.D., M.P.H.
Erika von Mutius, M.D.
University Children's Hospital, D-80337 Munich, Germany
erika.von. mutius@med. uni-muenchen. de 1
Devenny A ,Wassall H ,Ninan T ,Omran M ,Khan SD ,Russell G . Respiratory symptoms and atopy in children in Aberdeen: questionnaire studies of a defined school population repeated over 35 years. BMJ 2004;329:489-490
CrossRef | Web of Science | Medline
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