Network Analysis

Types of Transmission via Social Networks

Like the movement of exchangeable goods, the diffusion of pathogens through a human population traces the structure of social networks. The pattern of spread is jointly determined by the biology of the pathogen and the social structure that can support it, so different kinds of diseases travel along different structural routes. The plague, for example, is spread by a mobile vector of rats and fleas that makes for an efficient, long-lasting infectious vehicle. The disease can travel via long-distance transportation and trade routes even when travel is slow paced, with macroeconomic relations helping to structure the diffusion path. For influenza and measles, in contrast, transmission requires casual or indirect personal contact in a relatively short period of time. The spread of these infections is structured by locations of frequent collective activity, such as schools and supermarkets today, with transportation networks serving as potential bridges between communities and sparsely settled or less traveled routes serving as buffers. Finally, there are infections spread only by intimate or prolonged contact; STIs are a classic example. These diseases travel along the most selective forms of social networks, operating on what is comparatively a very sparse microstructure, with a typically modest duration of infection. The structure of sexual networks varies within and between societies, governed by local norms, power differentials, and oppositional subcultures. Here, as with other infectious diseases, the transmission network determines the potential for epidemics and the opportunities for prevention.

Network Epidemiology and Sexually Transmitted Infections

Network epidemiology offers a comprehensive way of thinking about individual sexual behavior and its consequences for STI transmission. Unlike other health-related behaviors (e.g., smoking) and safetyrelated behavior (e.g., using seat belts), behaviors that transmit STIs directly involve at least two people, as well as other persons to whom they may be linked. Understanding this process requires moving beyond the standard, individual-centered research paradigm. This has important implications for the analytic framework, data collection, and intervention planning.

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