component = set of persons who are all connected directly or indirectly

• more/smaller components prohibit transmission; linking components facilitate it

• Colorado Springs study - persons at high risk for HIV (Potterat et al.)

• no significant HIV epidemic in CO Springs, despite large amount of risky behavior and large number of partners

• why?

• infected persons in small components

• higher density - greater risk for epidemic transmission

• heterosexual sexual networks less efficient for transmission than homosexual/bisexual sexual networks or injection networks, independent of mode of transmission

• degree - how many ties to others

• betweenness - how many pairs of others a person connects, directly or undirectly

• closeness -  how many steps away from others

• high centrality of each type puts one at greater risk for infection

• prostitutes = high centrality; intersections/distribution points for transmission

• regions of network often correspond to geographic locations/areas

• mid 1990s Baltimore syphilis epidemic

• prior to epidemic, high prevalence areas = a few poor inner city neighborhoods

• public and private housing in inner city condemned, residents to different parts of city

• formed new partnerships in new areas, exporting syphilis to different parts of city

• before relocation, most partnerships within inner city; cyclical pattern of (re)infections

• urban renewal, etc. can splinter networks and promote epidemics

• serial monogamy vs. multiple ongoing, concurrent partnerships

• concurrency increases density

• sexual network structures in some African societies tend toward concurrency

• educational campaigns: "Love faithfully," "One partner at a time"

• to work, must hold to strict serial monogamy -- no recurrent, cyclical partners