Spatial Dynamics of Syphilis and Gonorrhea Transmission Among Sexual Networks and Core Groups in North Carolina

Syphilis and gonorrhea rates continue to increase and disproportionately affect vulnerable populations despite control efforts. Increased understanding of transmission dynamics in populations that sustain infection is urgently needed to better inform detection, surveillance, and control programs. We conducted spatial, latent class, and network analyses of de-identified and geomasked surveillance data from the North Carolina (NC) Division of Public Health to (1) evaluate the performance of proposed methods in identifying geographical core areas of syphilis and gonorrhea, (2) determine the relationship between syphilis core areas and the locations of individuals at high risk of onward transmission, and (3) characterize the relationship between social and geographical distances in a socio-sexual network associated with a syphilis outbreak in rural NC. In Aim 1, we used latent class analysis to estimate the sensitivity and specificity of four core area identification methods and found that accuracy varied by method and disease. For both gonorrhea and syphilis, the rate rank method combined the best overall accuracy with ease of implementation, suggesting it may be appropriate for most public health departments. In Aim 2, we used the results of Aim 1 and risk behavior data from disease intervention specialist interviews of reported syphilis cases to identify syphilis core areas and assess the probability of higher sexual activity among core areas cases compared to non-core area cases. We observed that higher activity cases were as likely to reside in non-core areas as core areas. While syphilis cases may be disproportionately concentrated in core areas, solely targeting interventions to core areas would unlikely lead to elimination due to transmission by high-activity core group members residing in non-core areas. In Aim 3, we found that spatially compact network structures depended on a complex interaction of characteristics not apparent at the individual or partnership levels. Despite being part of the same large outbreak, partnerships between similar persons formed distinct macro-level structures of varying spatial compactness that require different interventions to reduce transmission effectively. Multiple approaches are needed to help public health officials optimize intervention strategies and stem the current epidemic.Doctor of Philosoph