Translational epidemiology: developing and applying theoretical frameworks to improve the control of HIV and other sexually transmitted infections.

Abstract

The continued burden of disease caused by sexually transmitted infections (STIs), with 499 million cases of curable infections each year [1–3],constitutes a public health failure. Even in high-income countries, where extensive testing and treatment is available, STIs remain stubbornly endemic. It seems likely that this failure reflects our limited understanding of the complex individual, social, and cultural drivers of epidemics and of the interventions required in different contexts. Mathematical models of STI and HIV transmission have been used extensively to understand transmission dynamics, and to estimate and predict the impact of interventions in diverse settings. At a population level, contact rate, transmission likelihood and duration of infectiousness determine the potential for spread of STI and the distribution of values for these three factors determines the extent of epidemics. Such theoretically derived insights can be tested through epidemiological studies exploring the risks of individuals acquiring infection and how population level measures of risk relate to observed prevalence of infection. However, such studies also show that a range of social, demographic and economic variables influence an individual’ sr isk of infection and that populations have different patterns of STI incidence and prevalence. Theoretical frameworks can be constructed to embody hypotheses about how these factors interact. Such frameworks allow us to structure our knowledge of STI epidemiology and understand the causal pathways linking variables. Through a Wellcome Trust–funded research pro