Phase-specific network differences associated with the syphilis epidemic in Baltimore City, 1996-2000

Objectives: The objective of this study was to determine whether the syphilis epidemic in Baltimore City during the mid-1990s was associated with changes in sexual networks. Methods: Data on index cases of syphilis and their partners were collected from 1996 to 2000 and entered into CDC STD*MIS software. Unique pairs of dyads were used to create networks using SAS Interactive Matrix Language. PAJEK and UCINET were used to analyze the largest component from all years (1996-2000), during the epidemic (1997-1998), and after the epidemic (1999-2000). Results: Between 1996 and 2000, there were 3343 components containing 18,709 nodes. The 2 largest components were comprised of 1103 nodes and 125 nodes, respectively. From the period during the epidemic to after the epidemic, the average distance among reachable pairs, network centralization, number of n-cliques (n = 2, size = 3), and number of k-plexes (k = 2, n = 3) declined, whereas the block densities increased. Conclusions: Important differences exist between the sexual networks during and after the syphilis epidemic.