Studies on the spread of sexually transmitted infections (STIs) and HIV usually focus on individual risk factors such as the number of partners and condom use. But these factors do not fully explain epidemics. Social Network Analysis, a new approach, looks at how relationships between people in defined groups affect risk of disease spread. Valencia Remple is using this approach to conduct a sexual health survey of women who work in massage parlours. As part of the study, trained peer outreach workers are conducting in-depth interviews with workers to obtain information about their sexual behaviour, histories of STIs and the characteristics of their sexual partners. She is also measuring factors known to influence the spread of STIs, such as bridging. Bridging occurs when people in one defined group have sexual contact with members of different groups, which could introduce infections into previously uninfected populations. The results of this research could be used to develop targeted health services for this vulnerable and hidden population.