the importance of network structures in the epidemiology of HIV

The extent and structure of sexual networks have important consequences for the spread of sexually transmitted diseases such as HIV. However, very few datasets currently exist that allow a detailed investigation of sexual networks in sub-Saharan African settings where HIV epidemics have become generalized. In this paper, the authors describe the context and methods of the Likoma Network Study, one of the few studies that have collected extensive information on sexual networks in sub-Saharan Africa. They start by reviewing theoretical arguments and empirical studies emphasizing the importance of network structures in the epidemiology of HIV and other sexually transmitted infections. The island setting of this study is described, and the authors argue that the choice of an island as a research site limited potential biases that may make the collection of sexual network data difficult. Helleringer and colleagues then document their empirical strategy for the collection of sexual network data and the subsequent identification of sexual network partners. A description of the protocol for the collection of biomarker data (HIV infection) is provided. Finally, they present initial results relating to the socioeconomic context of the island, the size and composition of sexual networks, the quality of the sexual network data, the determinants of successful contact tracing during the Likoma Network Study, and the prevalence of HIV in the study population.

Although Likoma Island in Lake Malawi is 18 square kilometres and has a population of only 7000 people living in a dozen villages, it has contributed substantially to our understanding of the role of sexual networks in generalized epidemics. Only 7 of 1235 households refused to be interviewed about socioeconomic information and in the seven villages chosen for the sexual network survey (representing 50.9% of 18-35 year olds on Likoma), the participation rate was 88%. Whereas Demographic and Heath Surveys are ‘egocentric’, meaning that they rely on self-reports that have to be taken at face value, the Likoma Study is ‘socio-centric’. It provides detailed data on the extent and structure of sexual networks and evaluates data quality by determining rates of inter-partner agreement about sexual relationships. Understanding patterns of connectivity and overlap between relationships informs modelling of the sexual spread of HIV and can assist in the design of context-appropriate HIV prevention programmes. A big challenge is to explain how individuals are part of sexual networks, even if they themselves have only one partner.