Exclusive viral wheeze and allergic wheeze: evidence for discrete phenotypes

Abstract

To the Editors: There is a broad consensus that childhood wheezing illness consists of several distinct disease entities, but there is no agreement on their number or underlying mechanisms [1]. Commonly used phenotypic classifications are based on clinical or epidemiological criteria [2–6], and there has been little work focusing on causal mechanisms [1, 6, 7]. Trigger factors for wheezing episodes might be indicators of such mechanisms. In young children, wheeze is commonly triggered by respiratory viral infections (colds), physical factors associated with increased breathing (exercise, laughing, crying and excitement) or allergens (aeroallergens and food allergens). These triggers are increasingly used to define asthma phenotypes in young children [3, 5]. Despite this, there are few data on the way in which these triggers change in importance with age or whether different classes of triggers are independent. A close association between different classes of triggers in the same children would suggest a common underlying mechanism while a lack of association might reflect independent causal mechanisms. In this analysis, we describe changes in the prevalence of different parent-reported triggers of wheeze by age in 1–9 yr olds and report statistical associations between different classes of triggers (exercise, allergens and infection). We used data from the …