Title: A Molecular Epidemiologic Approach to Understanding the Spread of Disease
Description: Community-associated methicillin-resistant Staphylococcus aureus has been an increasing public health problem since its emergence in the 1990s and incarcerated populations are at disproportionately high-risk for colonization and infection. However, few studies have investigated why levels of S. aureus remain endemic in correctional settings in the absence of an outbreak. The overall objective of this dissertation was to evaluate S. aureus transmission in two maximum-security prisons using a molecular epidemiologic approach and data collected on over 2,700 inmates from 2009 – 2013. The objective of this dissertation was met using three aims. First, a systematic literature review was conducted to identify studies that used social network analysis (SNA) to evaluate infectious disease transmission via non-sexual/non-injection drug use contact pathways to detect influences of social networks on disease risk. Results of the review demonstrated that SNA approaches in infectious disease epidemiology are flexible and can be used to enhance traditional contact investigations, reveal granular patterns of transmission, evaluate influences of high-risk behaviors and activities, and identify both protective and causal effects resulting from context-specific social interactions.

Second, changes in the distribution and diversity of S. aureus isolates with increasing length of incarceration were assessed. The results revealed some evidence for S. aureus transmission based on greater representation of certain strains; however, the genetic diversity of S. aureus was high regardless of length of time served. Third, the influence of social interactions among prison inmates on S. aureus colonization status was examined using SNA. The results showed that S. aureus colonized inmates were more likely to spend time in social groups and that the mechanisms of transmission differed for men and women. For women, the association was driven by being centrally located in the social network and for men it was driven by higher proportions of colonized inmates in close proximity. Overall, the results of this dissertation support the hypothesis that S. aureus is transmitted within prisons as a result of direct skin-to-skin contact and/or exposure to contaminated environmental surfaces.

However, the results also demonstrate that, in the absence of an outbreak, S. aureus transmission within prisons is low indicating that endemic levels of S. aureus are primarily maintained by the constant introduction of clones into prisons from jails and the community.