Associations between respiratory symptoms, bronchial response to methacholine, and atopy in two age groups of schoolchildren.
Data on respiratory symptoms were obtained on 2503 schoolchildren aged 7 and 11 in Southampton by means of a self administered parental questionnaire. Children were classified into seven symptom groups from which 330 were tested for bronchial responsiveness to less than or equal to 6.4 mumol methacholine and skin tested for the presence of atopy. The symptoms of wheeze, cough, and shortness of breath were all significantly associated both with each other and bronchial responsiveness to methacholine but only wheeze was associated with atopy. The association of wheeze with both bronchial responsiveness to methacholine and atopy remained highly significant when controlling for the symptoms of cough and shortness of breath. Neither cough nor shortness of breath, however, were significantly related to bronchial responsiveness to methacholine when controlling for the symptom of wheeze. This study therefore calls into question the epidemiological relevance of these two symptoms as diagnostic features of asthma, particularly in the absence of wheeze, although they may be useful indicators of morbidity. Wheeze was not related to bronchial responsiveness to methacholine in the absence of atopy or to atopy in the absence of bronchial responsiveness to methacholine but was strongly related to the combination of the two phenomena. The presence of these three characteristics could therefore indicate a discrete disease entity. The decrease in the prevalence of cough between 7 and 11 years appeared to be mirrored by a similar decrease in the prevalence of wheeze when the symptom was not associated with the combination of bronchial responsiveness to methacholine and atopy. On the basis of these findings and those of others we suggest that the latter group may represent children with a separate disease entity(ies) or with residual symptoms secondary to acute viral or other infections of the lower respiratory tract.