• social epidemiology
• sexually transmitted infections
• social networks

Prevalence and incidence of sexually transmitted infections (STIs) vary across societies¹ and across subpopulations defined by age, race-ethnicity, and socioeconomic status.^{2, 3} The efforts to account for such variation and explain it, that can be found in the STD literature, have in general not differentiated between individual and population level health, or between population and individual level determinants of individual STD outcomes.⁴ Perhaps this pattern reflects the predominant paradigm in modern epidemiology which has been termed the “risk factor” paradigm and has been linked to “biomedical individualism” as its underlying theoretical foundation.^{5, 6} This theoretical approach views populations simply as reflective of individual cases while considering social determinants of disease to be at best secondary, if not irrelevant.⁷ In the past several years, the risk factor paradigm in epidemiology has been seriously challenged by leading epidemiologists ^{8, 9} and a new paradigm that would emphasise the broader context of individual risk factors has been called for. It has been suggested that whereas traditional epidemiologists ask the question “Why are some individuals healthy and others not?” the social epidemiologist is concerned with the question “Why are some societies healthy while others are not?”¹⁰ Social epidemiology has focused on features of the economy, culture, politics, and the law. Examples of societal characteristics that have received attention include macroeconomic factors such as poverty, unemployment, and income distribution; and features of social relationships such as social cohesion, social exclusion, and sex and race relationships.¹¹ Also, a renewed interest in effects of neighbourhood environments on morbidity and mortality has emerged.^12–14

Work in social epidemiology has emphasised neighbourhoods and the community; and considerations of social capital and collective efficacy have usually been applied to chronic diseases, mortality, violence, and …