摘要：Objectives. We explored the effects of social determinants of health on pandemic H1N1 2009 influenza severity and the role of clinical risk factors in mediating such associations. Methods. We used multivariate logistic regression with generalized estimating equations to examine the associations between individual- and ecological-level social determinants of health and hospitalization for pandemic H1N1 2009 illness in a case-control study in Ontario, Canada. Results. During the first pandemic phase (April 23–July 20, 2009), hospitalization was associated with having a high school education or less and living in a neighborhood with high material or total deprivation. We also observed the association with education in the second phase (August 1–November 6, 2009). Clinical risk factors for severe pandemic H1N1 2009 illness mediated approximately 39% of the observed association. Conclusions. The main clinical risk factors for severe pandemic H1N1 2009 illness explain only a portion of the associations observed between social determinants of health and hospitalization, suggesting that the means by which the social determinants of health affect pandemic H1N1 2009 outcomes extend beyond clinically recognized risk factors. Similar to seasonal influenza, most cases of pandemic H1N1 2009 influenza were relatively mild; however, certain groups of individuals were at a higher risk of complication and severe disease than were others. Information from early pandemic H1N1 2009 case series indicated that risk factors typically associated with severe seasonal influenza, including underlying conditions such as pulmonary or cardiac disease, diabetes, and pregnancy, were observed among individuals very ill with pandemic H1N1 2009; however, unlike seasonal influenza, severe pandemic H1N1 2009 affected children of all ages and young adults, many of whom were previously healthy. 1–6 Obesity and morbid obesity were also recognized as risk factors. 2,7,8 In Ontario, Canada, a case-control study was conducted as part of a pan-Canadian approach to pandemic H1N1 2009 research. The purpose of this study was to identify risk factors for pandemic H1N1 2009 infection requiring hospitalization (L. C. R. and N. C., unpublished data, 2010). 9 Many of the risk factors identified in our study and others, notably the presence of chronic conditions such as diabetes 10–12 and obesity 13,14 and health behaviors such as smoking 15,16 and accessing health care, 17 are known to be influenced by the social determinants of health. The social determinants of health are social and economic conditions, such as income, education, employment, and social support, that influence the health of individuals and communities. Disparities in these conditions are reflected in a gradient of socioeconomic status (SES), which, in turn, is associated with inequalities in health. It is widely recognized that individuals at the lower end of the SES gradient experience poorer health and a reduced life expectancy compared with more advantaged groups. 18–20 We were therefore interested in exploring the effects of the social determinants of health on pandemic H1N1 2009 severity in Ontario and the role of clinical risk factors in mediating any such associations. In addition to individual characteristics, contextual socioeconomic factors, such as neighborhood conditions, influence health outcomes. A majority of studies investigating neighborhood effects on health have found significant associations between measures of area SES and health outcomes, such as self-reported health and mortality, that are independent of the effects of individual socioeconomic characteristics. 21,22 The mechanisms by which neighborhood characteristics affect the health of individuals are not fully understood, but there are several potential pathways through which ecological exposures may affect the severity of influenza infection. For example, neighborhood problems such as vandalism, illegal drug use, noise, and litter are sources of psychological stress for residents, 23–25 and psychological stress is known to influence immune function. 26,27 Neighborhood-associated psychological stress could therefore place individuals at increased risk of severe influenza illness. Indeed, Cohen et al. demonstrated that among individuals experimentally infected with influenza, those reporting high psychological stress before inoculation experienced more severe illness than did individuals with low stress. 28 Another possibility is that environmental exposures, such as air pollution, contribute to an individual’s risk for severe infection. Traffic-related air pollution is associated with incident asthma, 29–32 and asthma was identified as an important risk factor for severe pandemic H1N1 2009 outcomes, including hospitalization. 33 This evidence demonstrates that the social determinants of health exert influence on health at the ecological level as well as at the individual level. We examined the effects of individual- and ecological-level social determinants of health on pandemic H1N1 2009 severity, as indicated by hospitalization, in Ontario, Canada. Furthermore, we explored the role of known clinical risk factors for severe pandemic H1N1 2009 infection in mediating any such associations. A few studies have investigated the associations between the social determinants of health and respiratory infection outcomes, such as healthcare utilization 34 and hospitalization. 35–37 The outcomes measured in these studies are not specific to influenza and include outcomes from all or acute respiratory infections 35 and influenza and pneumonia diagnoses combined. 37 Measuring influenza-specific outcomes is challenging because of the nonspecific presentation of illness and the limited use of laboratory diagnostic testing for medical management. The prevalent use of diagnostic testing for influenza during the H1N1 2009 pandemic, therefore, provided a unique opportunity to examine the effect of the social determinants of health on influencing hospitalization specifically because of this novel strain of influenza.
