[Contribution of epidemiologic research to the knowledge on the etiology of asthma]

The results of the European Community Respiratory Health Survey (ECRHS) represent one of the most important contributions to the understanding of the risk factors for asthma and its natural history in young adult population. ECRHS has documented up to tenfold regional differences in the prevalence of respiratory symptoms, asthma, atopic sensitisation and bronchial responsiveness: the UK, the USA, Australia and New Zealand had the highest rates. The ECRHS data highlighted the importance of childhood exposure on atopic sensitisation, showing that factors associated with exposure to micro-organisms in childhood reduce the likelihood to be atopic in adulthood. Local results documented the presence of an increasing trend in asthma and allergy from rural to urban sites. The association found between the use of gas cooking with subjective and objective markers of respiratory morbidity in women, raised the hypothesis that exposure to indoor pollutants, such as NO2, could increase the susceptibility for asthma. ECRHS data also allowed a retrospective analysis of asthma occurrence, pointing out that the incidence has increased in the last generations. Furthermore, the analysis of asthma incidence by sex and age suggested a potential role of airway calibre, in addition to hormonal factors, in explaining the greater susceptibility to asthma in women than in men after the age of fifteen.