Although many diseases spread so easily between humans that someone could be infected by any of his or her daily social contacts, such is not the case for sexually transmitted diseases. Most of us have a very limited number of concurrently ongoing sexual partnerships, and thus the contact network over which sexually transmitted diseases spread tends to be very sparsely connected. The exact structure of these sexual networks plays an important role in how easy and fast sexually transmitted diseases spread through a population, and how effective various health care interventions will be.
Schmid BV, Kretzschmar M (2012) Determinants of Sexual Network Structure and Their Impact on Cumulative Network Measures. PLoS Comput Biol 8(4): e1002470. http://dx.doi.org/10.1371/journal.pcbi.1002470