Reporting of common respiratory and atopic symptoms has increased

Editor—Per Magnus and Jouni J K Jaakkola question reports of an increased prevalence of wheezing illness and asthma in recent population studies.1 In the three Aberdeen surveys the questions relating to asthma, shortness of breath, eczema, and hay fever were identical; the question on wheeze was modified between the first and second studies.2 The responses to the four identical questions showed significant and continuing rises in the prevalence of attacks of shortness of breath and awareness of a diagnosis of asthma or eczema.

Magnus and Jaakkola suggest that future surveys should include objective assessments of asthma, including tests of non-specific bronchial hyperresponsiveness and skin prick tests. Atopy as defined by a positive result of a skin prick test with common inhaled allergens is so common in the general population (up to half of subjects) that this is unlikely to be informative. Although non-specific bronchial hyperresponsiveness is reasonably reproducible when applied to adult asthmatic populations derived from hospital, it is a much less stable marker in population based studies of children.3

The authors raise an interesting point concerning the changing labelling of wheezing illness in recent years. Whereas before 1970, certainly in Britain and Australia, recurrent wheeze was categorised as either asthma or wheezy bronchitis, this distinction has not been made in more recent surveys. Consequently, important information on causation and prognosis may have been obscured, as different respiratory tract symptoms such as breathlessness, cough, and wheeze with or without atopic features may underlie different clinical syndromes4 with different prognostic implications.5

We have therefore looked again at the results of the three Aberdeen surveys to examine changes in the prevalence of asthma and of wheezy bronchitis, using the original definition of “wheeze only in the presence of upper respiratory tract infection.” Whereas the prevalence of respiratory symptoms and reported diagnoses of atopy, including wheeze associated with other atopic disease, has shown a consistent increase, the prevalence of wheezy bronchitis has remained remarkably stable (1).

Either our population has become extremely sophisticated in translating increased publicity about asthma into increased reporting of common respiratory and atopic symptoms or these symptoms have indeed increased in our community over the past 30 years. The population stability of wheeze associated with upper respiratory tract infection and the increased reporting of atopic symptoms suggest that changing environmental factors are associated with the latter but not with the former.

Labelling of cough alone as asthma may partially explain increase

Editor—Per Magnus and Jouni K Jaakkola give several factors that may contribute to the overreporting of asthma and hence the apparent increase in prevalence.1 We wish to add two further possible factors. Firstly, in the past decade the symptom of cough alone has increasingly been used to diagnose asthma.2 There are several problems with this: the repeatability of questions on cough in epidemiological studies is poor, the subjective reporting of cough is unreliable,2 and cough alone is a poor marker of asthma in both epidemiological and clinical studies.3 Therefore the labelling of cough alone as asthma may partially explain the increase. Secondly, even studies that included an objective measure of airway hyperresponsiveness in their definition of asthma need to be interpreted with care. Peat et al reported a significant increase in airway hyperresponsiveness to histamine in Australian children.4 This may, however, be partly explained by a change in the method of delivering histamine.5 Thus even objective methods can be misleading.