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[quote]Here is a very important paper about the risk behaviour causing AIDS and some tips for tackling it.

How do sexual networks affect HIV/STI prevention?

Do networks affect transmission?
The different ways persons select partners affect how quickly HIV/STDs can spread. Exclusively monogamous persons are, by definition, not part of a sexual network. If both are HIV-negative they remain so.

Serial monogamists are persons who go from relationship to relationship one at a time. If they have unprotected sex, they have a higher risk of HIV/STDs than exclusively monogamous persons. Earlier partners’ risk may affect later partners.

Concurrent relationships involve having more than one sexual partner in a given period and going back and forth between them. This increases the probability for transmission, because earlier partners can be infected by later partners. Further, they can serve as “nodes”, connecting all persons in a dense cluster, creating highly connected networks that facilitate transmission. Concurrent partners can connect each of their respective clusters and networks as well. Concurrency alone can fuel an epidemic even if the average number of partners is relatively low.2

The two networks above show that what matters is not simply risk behavior, but risk configuration. Each has 8 persons (circles) connected into 9 relationships. Two persons each have 3 partners, and the other six each have 2 partners. Yet transmission will be less efficient in network A, and prevention will be more difficult in network B. In A, in just two steps from the index person, half the network can be infected and half spared; in B, two steps can result in everyone being infected except for the person on the extreme right. In A, sparing half the population from exposure requires cutting one bridge, while in B, it requires cutting three bridges. In a word, for epidemics, network structure is destiny.3