• Asthma
• children
• definitions
• Ecuador
• asthma epidemiology

Drs Marsh and colleagues are essentially correct in saying that the word ‘wheeze’ rather than ‘asthma’ may have been more appropriate in the title of our paper. Not all wheeze is asthma but, given the lack of a widely agreed definition for asthma, we chose to use a simple but widely used definition (wheeze in the past 12 months) in this Ecuadorian study to estimate prevalence. As the authors will have seen from the abstract, the aim of the study was to investigate risk factors for atopic and non-atopic wheeze illness to understand better those that may cause or protect against asthma in the study population.1

All subjects with wheeze in the past 12 months had a history of wheeze ever. A high proportion of children in the study population had a history of wheeze ever (32.5%), most of which could be attributed to respiratory tract infections in earlier childhood (unpublished findings of cohort and cross-sectional studies of children aged up to 5 years in the same population in Esmeraldas Province, Ecuador) and, as a definition of asthma, would be subject to much greater misclassification. We did consider a more complex definition to increase specificity but decided against this because of a lack of validation.

Wheeze in the past 12 months is now the most widely used definition for asthma in epidemiological studies2 3 and, although we agree it may be subject to some misclassification, such a definition has three important advantages: (1) simplicity, permitting widespread use in epidemiological studies; (2) the definition is more inclusive and, where a word for the symptom exists in the local language that is linked culturally with asthma, may be less subject to bias in poor populations (see below); and (3) its wide use permits comparison between studies of the role of potential risk factors and more powerful analyses across studies of potential risk factors with a wide range in the prevalence of exposure. Examples of the latter are phases I–III of the International Study of Asthma and Allergies in Childhood (ISAAC) which have made important contributions to our understanding of asthma internationally.4 Furthermore, other definitions may be more prone to misclassification bias. For example, a doctor diagnosis of asthma is widely used5 6 but is unlikely to be helpful in populations with very limited access to healthcare such as the population where we conducted this research in rural Ecuador.

The distinction between different asthma/wheeze phenotypes remains an area of considerable debate7 and such phenotypes may not necessarily be uniform across different populations. Given the lack of consensus on how to measure asthma in epidemiological studies, we believe that wheeze in the past 12 months is as good as any definition presently available, but certainly agree that such a definition has its limitations.