Advancing a multilevel framework for epidemiologic research on asthma disparities.

Our understanding of asthma epidemiology is growing increasingly complex. Asthma outcomes are clearly socially patterned, with asthma ranking as a leading cause of health disparities among minority and low socioeconomic groups. Yet, the increasing prevalence and marked disparities in asthma remain largely unexplained by known risk factors. In the United States, asthma disproportionately affects nonwhite children living in urban areas and children living in poverty. Low socioeconomic status (SES), ethnic minority group status, and residence in an inner-city environment are closely intertwined in the United States, making it a challenge to fully disentangle the independent effects of each of these characteristics on asthma morbidity. In addition, studies show geographic variation in asthma outcomes across large cities and neighborhoods within cities that cannot be explained by economic factors alone. Although more limited data are available, studies in rural areas also suggest the stratification of risk based on SES and the proportion of minorities. Among low-SES areas, those with predominantly minority, segregated populations seem especially burdened. Marginalized populations of lower socioeconomic position are disproportionately exposed to irritants (eg, tobacco smoke), pollutants (eg, diesel-related particles), and indoor allergens (eg, cockroach and mouse allergen). Moreover, these marginalized individuals may also live in communities that are increasingly socially toxic, which, in turn, may be related to the increased experience of psychosocial stress that may influence asthma morbidity. Epidemiologic trends suggest that asthma may provide an excellent paradigm for understanding the role of community-level contextual factors in disease. Specifically, a multilevel approach that includes an ecological perspective may help to explain heterogeneities in asthma expression across socioeconomic and geographic boundaries that, to date, remain largely unexplained. Traditionally, asthma epidemiology has focused on individual-level risk factors and family factors. Far less attention has been given to the broader social context in which individuals live. A multilevel approach that explicitly recognizes the embedding of asthma within its biological, psycho-socioeconomic, environmental, and community contexts, is likely to provide a better understanding of asthma disparities at different stages in the life course. Is it simply asthma disparities or is it social disparities in asthma?