The burden of asthma: weighing the community risk against individual risk.

During the past few years findings from two studies—the International Study of Asthma and Allergies in Childhood (ISAAC) 1 and the European Community Respiratory Health Survey (ECRHS) 2 —seem to have dominated much of the thinking about the geographical variations in the prevalence of asthma. These studies suggest important variations by geographical site in diVerent countries and, to a lesser extent, in study centres within countries. However, these studies only raise new questions as to how geographical factors contribute to the aetiology of asthma. For example, are the geographical variations in the prevalence of asthma caused by unique exposures to disease causing agents found only in local environments? Do diVerences in geographical location in some way alter host susceptibility? Do local environmental conditions, either physical or sociocultural, alter the host/agent interactions in ways that are critical to the expression of this condition? In this issue of Thorax Duran-Tauleria and Rona 3 further elucidate how social and physical environmental factors may explain some of the geographical expression of asthma prevalence. Their study focuses on the diVerences in asthma and respiratory symptoms among three populations—two nationally representative samples of English and Scottish children and a third sample of children living within the inner cities of England. The authors found a higher prevalence of children with persistent (as opposed to occasional) wheeze within the inner city population than in the other two sampled populations. They also found that the prevalence of asthma attacks was higher in the non-inner city sample of English children than in the other two groups. Social and physical environmental factors—mainly social deprivation (as measured by the Townsend score)—seemed to explain much of the geographical variation in children with persistent wheezing. This finding held even after adjusting the analysis for many of the well known risk factors that might otherwise have explained these diVerences such as age, sex, parental atopy, and maternal smoking. The importance of social and physical environmental factors in disease expression is well known and has been studied extensively for many health conditions, including asthma. A number of studies suggest an association between higher asthma morbidity/mortality rates and geographical areas of lower socioeconomic standing. The literature on the eVects of social environmental factors on the prevalence of asthma is less definitive, but there have been several studies that suggest findings similar to those of Duran-Tauleria and Rona. Yet this current study also provides new insights into the …