Sexual network position and risk of sexually transmitted infections

Objectives: A population-based sexual network study was used to identify sexual network structures associated with sexually transmitted infection (STI) risk, and to evaluate the degree to which the use of network-level data furthers the understanding of STI risk. Methods: Participants (n=655) were from the baseline and 12-month follow-up waves of a 2001-2 populationbased longitudinal study of sexual networks among urban African-American adolescents. Sexual network position was characterised as the interaction between degree (number of partners) and two-reach centrality (number of partners' partners), resulting in the following five positions: confirmed dyad, unconfirmed dyad, periphery of non-dyadic component, centre of star-like component and interior of non-star component. STI risk was measured as laboratory-confirmed infection with gonorrhoea and/or chlamydia. Results: Results of logistic regression models with generalised estimating equations showed that being in the centre of a sexual network component increased the odds of infection at least sixfold compared with being in a confirmed dyad. Individuals on the periphery of non-dyadic components were nearly five times more likely to be infected than individuals in confirmed dyads, despite having only one partner. Measuring network position using only individual-based information led to twofold underestimates of the associations between STI risk and network position. Conclusions: These results demonstrate the importance of measuring sexual network structure using network data to fully capture the probability of exposure to an infected partner.