Examining the Role of Network Structure in HIV Transmission among People who Inject Drugs in the Philippines: A Tale of Two Cities Public Deposited

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  • March 21, 2019
  • Siripong, Nalyn
    • Affiliation: Gillings School of Global Public Health, Department of Epidemiology
  • While HIV growth has slowed globally, new HIV epidemics among people who inject drugs (PWID) continue to emerge [1-4]. These epidemics are marked by periods of unusually rapid growth, where HIV increases from virtually 0% to 20-50% within 3-6 years [5-6]. In concentrated epidemics, HIV epidemics among PWID could precipitate larger-scale heterosexual epidemics [7-10], which further underscores the urgent need to find effective ways to reach and deliver prevention services to PWID. We studied the emergence of HIV among PWID in two cities in the Philippines. The epidemic began in Cebu City, where HIV prevalence grew from 0.6% in 2009 to 50% in 2010 [11]. Expanded surveillance in neighboring Mandaue City found more limited spread of infection, with HIV prevalence reaching only 3.5% in 2011[12], rising to 38% in 2013 [13]. We used exponential random graph models (ERGMs) to simulate network structures and assess whether differences in network structure could explain variation in HIV prevalence patterns in the two cities. We further analyzed genetic sequencing data to consider the extent of overlap or linkage between networks. Simulated networks showed distinct differences between the two cities. We found smaller network components in Mandaue than in Cebu (1082 v 2980), which may explain the limited spread of HIV there. We also found that Cebu networks exhibited higher degree (21.5 v 10.8), lower clustering (0.29 v 0.39), and shorter average paths (3.3 v 3.8), all of which would facilitate rapid spread of infection across the network. A phylogenetic tree showed high bootstrap support for a large cluster of HIV infections (N = 172), predominantly from PWID from Cebu and Mandaue (85%), which suggests that HIV infection in the two cities arose from a common source infection. This work suggests that the emergence of a rapidly growing epidemic among PWID in Cebu City spread to Mandaue City, but network structures initially prevented growth of infection. The fragmented network in Mandaue initially prevented penetration of infection into the connected portion of the network. Future work applying transmission modeling to these networks may offer important insights to the role of networks on HIV in these populations.
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  • In Copyright
  • Dennis, Ann
  • Pence, Brian
  • Powers, Kimberly
  • van Rie, Annelies
  • Moody, James
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017

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