Characteristics of the Largest Network Component of Individuals With or Exposed to Early Syphilis in Central Indiana: 2016 to 2017.

BACKGROUND: The surge of syphilis infections in the United States continues. This study examined the sexual networks of early syphilis cases to determine whether repeat infection, demographics, or behaviors differed among network components (groups of connected persons). METHODS: We examined a retrospective cohort of all early syphilis cases in Central Indiana reported from January, 1, 2016, to January 24, 2018, in the state's reporting database. Cases were linked to their sexual partners and analyzed using UCINET and NetDraw. Attributes of network members were derived from disease intervention specialist interviews. Repeat cases were defined as those who also had ≥1 early syphilis infection at any time between 2011 and 2017. The resulting network included 1140 unique individuals, 436 cases and 704 contacts. We compared members of the main component, that is, the largest one, with the rest of the network using multiple logistic regression and network analyses. RESULTS: The network formed 197 separate components. The main component contained 473 individuals (41% of the cohort). Main component members were more likely to have repeat early syphilis, gonorrhea, Black race, male sex, and a history of methamphetamine use, and be HIV positive by multiple logistic regression. Results from multiple centrality measures indicated persons who might be most effective at disseminating information or fragmenting the main component. CONCLUSIONS: Network analysis identified a group of linked individuals most likely to be reinfected with syphilis in Central Indiana. Further investigation is needed to determine whether engaging such a high-risk group could better focus resources and decrease infections.