The social epidemiology of human immunodeficiency virus/acquired immunodeficiency syndrome.

Social epidemiology is defined as the study of the distribution of health outcomes and their social determinants (1). It builds on the classic epidemiologic triangle of host, agent, and environment to focus explicitly on the role of social determinants in infectious disease transmission and progression. These determinants are the “features of and pathways by which societal conditions affect health” (2, p. 697). Early studies of human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS) focused on individual characteristics and behaviors in determining HIV risk, an approach that Fee and Krieger (3) refer to as “biomedical individualism.” Biomedical individualism is the basis of risk factor epidemiology; by contrast, the social epidemiology perspective emphasizes social conditions as fundamental causes of disease (4) (table 1). Social epidemiologists examine how persons become exposed to risk or protective factors and under what social conditions individual risk factors are related to disease. Social factors are thus the focus of analysis and are not simply adjusted for as potentially confounding factors or used as proxies for unavailable individual-level data. Social factors are indeed critical to understanding nonuniform infectious disease patterns that emerge as a result of the dependent nature of disease transmission or the idea that an outcome in one person is dependent upon outcomes and exposures in others (5, 6). Contact patterns that enhance HIV/AIDS vulnerability may be conceptualized at multiple levels. Figure 1 distinguishes determinants of HIV/AIDS at three levels: individual, social, and structural. Individual factors include biologic, demographic, and behavioral risk factors that may influence the risk of HIV acquisition and disease progression. Social-level factors include critical pathways by which community and network structures link persons to society. These structures are central to understanding the diffusion and differential distribution of HIV/AIDS in population subgroups. Structural-level factors include social and economic factors, as well as laws and policies. These factors, in turn, affect HIV transmission dynamics and the differential distribution of HIV/AIDS. Infectious disease epidemiology provides models of the mechanisms through which social determinants affect HIV transmission (7). For example, the basic reproductive number of an infectious disease, R0 (8), describes secondary infections that arise from a primary infection. In the equation R0 = βCD, β is the probability of infection per contact, C is the number of contacts, and D is the duration of infectivity. The goal of intervention efforts is to reduce the empirical value of these terms by modifying the social conditions under which individual risk factors lead to disease. Examples of factors that affect the component terms of R0 in HIV epidemiology are presented in table 2. In this review, we present existing evidence linking social and structural determinants to HIV/AIDS. In addition, we discuss the implications of these findings for future social epidemiology research on HIV/AIDS as well as the design of more effective HIV/AIDS interventions.