Background Despite remarkable progress in the scientific understanding of the biological characteristics of the pathogens, pathogenesis and immunology, human sexual behaviour and population transmission dynamics, there are still considerable knowledge gaps regarding the heterogeneity and determinants of epidemics of sexually transmitted infections (STI) and HIV. To understand more fully the causes of STI and HIV epidemics it is necessary to reconcile individual and population approaches and bring together sociological and biomedical streams of research.

Methods This study examined the implications of approaching the study of STI and HIV epidemics from the perspective that individual and population-level characteristics and interactions result in emergent properties and structural patterns that cannot be easily predicted. In addition to offering examples from the research literature, female sex work is analysed as an example of a complex adaptive system and the implications for STI and HIV epidemics are examined in that context.

Results Previous research in this field has provided compelling examples of how the complex interplay of individuals and resulting structural patterns including sexual networks can influence the patterns of emergence and the trajectory of STI and HIV epidemics.

Conclusions Approaching the study of STI and HIV epidemics as emergent phenomena arising from complex interactive systems with diverse structural patterns offers a promising avenue for developing a more coherent understanding of these epidemics. It would also promote consilience between sociological, population and biomedical disciplines that could open new vistas for the science of public health.