Background: In most epidemiological surveys the estimated prevalence of asthma is based on questionnaire responses, which may depend on the individual's perception as well as medical consulting habits in a given population. Therefore, measurement of bronchial hyper-responsiveness as a key feature of asthma has been suggested as an objective parameter for asthma.
Objective: The aim of the present study was to validate questionnaire responses on asthma and wheeze against bronchial response to hypertonic saline (HS) (4.5%) in populations previously shown to have a lower prevalence of asthma and allergies: farmers' children and children from anthroposophic families.
Methods: Children whose parents had completed a written questionnaire in the cross-sectional PARSIFAL-study were drawn from the following four subgroups: 'farm children' (n=183), 'farm reference children' (n=173), 'Steiner schoolchildren' (n=243) and 'Steiner reference children' (n=179). Overall, 319 children with wheeze in the last 12 months and 459 children without wheeze in the last 12 months performed an HS challenge.
Results: Odds ratios, sensitivity, specificity, likelihood ratios and measures of association did not differ significantly between the four subgroups. The correlation between the bronchial response to HS and wheeze and asthma questions was moderate and similar for farm children, farm reference children, Steiner schoolchildren and Steiner reference children (kappa for 'wheeze': 0.25, 0.33, 0.31, 0.35, respectively, P=0.754, kappa for 'doctor's diagnosis of asthma': 0.33, 0.19, 0.33, 032, respectively, P=0.499).
Conclusion: The findings from this study suggest that the reliabilitiy of questionnaire responses on asthma and wheeze is comparable between farmers' children, children raised in families with anthroposophic lifestyle and their respective peers.