Epidemiologic and socioeconomic aspects of allergic diseases.

It is evident that asthma and the other allergic diseases constitute a health problem of international scope. There is a need for well-designed, large-scale, prospective epidemiologic studies designed to define precisely the magnitude of the worldwide problem created by allergic disorders. Most studies to date have been small and have involved special groups rather than the entire population. With the exception of data reported from developing countries, prevalence rates for childhood asthma are noted to be both increasing and higher than adult rates. While exact reasons are not known, the state of development of immune system regulation and hyperreactivity to allergens encountered in early life may play a role. Whether the actual prevalence and incidence of allergic diseases in children are increasing or whether this observation represents a phenomenon resulting from improved diagnostic methods and recognition of these disorders needs to be established. Paradoxically, despite advances in treatment, the severity of asthma and allergic diseases appears to be increasing. Accordingly, it is especially important to search for the factors that lead to the expression of immune and hypersensitivity mechanisms. Differences in rural and urban populations appear to be real and suggest the need to examine the factors of indoor and outdoor environments created by air pollution, crowding, and allergen exposure and the demands made on the immune system by frequency of challenge by respiratory tract infections. Still among the unknowns is the effect on the natural history of allergic disease after changes in urban-rural residences in countries in which helminth infections are not hyper IgE-stimulating factors. The creation of new occupationally related allergens at worksites and the contribution of industrialization to the deterioration of the natural environment needs to be adequately assessed. Whether breast feeding may have an effect on either the prevention or delayed emergence of food allergies in children requires documentation by long-term prospective studies based on objective testing. A possible relationship between respiratory tract infection and the development of asthma is exemplified by clinical observations. The emergence of asthma in infants increases with successive episodes of bronchiolitis; triggering of asthmatic attacks by acute respiratory tract viral infections is a common occurrence, especially during childhood years; and chronic adult onset asthma is often preceded or accompanied by chronic sinusitis or complicated by lower respiratory tract infection.(ABSTRACT TRUNCATED AT 400 WORDS)