Occurrence of asthma, nonspecific bronchial hyperresponsiveness and atopy. Insights from cross-sectional epidemiologic studies.

Data from various different types of cross-sectional studies are reviewed in order to examine hypotheses about the etiology of asthma and to more precisely define its relationship with nonspecific bronchial hyperreactivity (NSBH). Although cross-sectional studies have not clarified the precise etiologic links, they have established that NSBH and atopy are linked to the occurrence of asthma and to each other. In children, evidence supports the hypothesis both that atopy is a cause of asthma and that atopic diathesis is the most frequent trigger for NSHB. In adults, the associations are more complex, although in a small subset findings are similar to those in children. It is concluded that further general population-based or clinical epidemiologic cross-sectional studies based on questionnaires will contribute little more to explaining these associations. Criteria are presented for the further application of case-control studies to maximize their use in examining hypotheses of asthma etiology.