title: Hepatitis C transmission and treatment as prevention - The role of the injecting network.
abstract: BACKGROUND
  The hepatitis C virus (HCV) epidemic is a major health issue; in most developed countries it is driven by people who inject drugs (PWID). Injecting networks powerfully influence HCV transmission. In this paper we provide an overview of 10 years of research into injecting networks and HCV, culminating in a network-based approach to provision of direct-acting antiviral therapy.
  
  
  METHODS
  Between 2005 and 2010 we followed a cohort of 413 PWID, measuring HCV incidence, prevalence and injecting risk, including network-related factors. We developed an individual-based HCV transmission model, using it to simulate the spread of HCV through the empirical social network of PWID. In addition, we created an empirically grounded network model of injecting relationships using exponential random graph models (ERGMs), allowing simulation of realistic networks for investigating HCV treatment and intervention strategies. Our empirical work and modelling underpins the TAP Study, which is examining the feasibility of community-based treatment of PWID with DAAs.
  
  
  RESULTS
  We observed incidence rates of HCV primary infection and reinfection of 12.8 per 100 person-years (PY) (95%CI: 7.7-20.0) and 28.8 per 100 PY (95%CI: 15.0-55.4), respectively, and determined that HCV transmission clusters correlated with reported injecting relationships. Transmission modelling showed that the empirical network provided some protective effect, slowing HCV transmission compared to a fully connected, homogenous PWID population. Our ERGMs revealed that treating PWID and all their contacts was the most effective strategy and targeting treatment to infected PWID with the most contacts the least effective.
  
  
  CONCLUSIONS
  Networks-based approaches greatly increase understanding of HCV transmission and will inform the implementation of treatment as prevention using DAAs.
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; Infectious Diseases Unit, The Alfred Hospital, 55 Commercial Road, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventative Medicine, Monash University, 89 Commercial Road, Melbourne, Victoria 3004, Australia; Centre for Research Excellence in Injecting Drug Use, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia. Electronic address: hellard@burnet.edu.au.
authors.forename: Margaret
authors.initials: M
authors.lastname: Hellard
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; Victorian Infectious Disease Service, Royal Melbourne Hospital, Royal Parade, Parkville, Victoria 3050, Australia; Department of Medicine, University of Melbourne, Victoria 3010, Australia.
authors.forename: Emma
authors.initials: E
authors.lastname: McBryde
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventative Medicine, Monash University, 89 Commercial Road, Melbourne, Victoria 3004, Australia; Centre for Research Excellence in Injecting Drug Use, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Rachel
authors.initials: R
authors.lastname: Sacks Davis
authors.affiliation: Melbourne School of Psychological Sciences, University of Melbourne, Victoria 3010, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Rolls
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; National Drug Research Institute, Faculty of Health Sciences, Curtin University (Melbourne Office), 19-35 Gertrude St, Fitzroy, Victoria 3065, Australia; Department of Medicine, University of Melbourne, Victoria 3010, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Higgs
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventative Medicine, Monash University, 89 Commercial Road, Melbourne, Victoria 3004, Australia; Centre for Research Excellence in Injecting Drug Use, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Campbell
authors.initials: C
authors.lastname: Aitken
authors.affiliation: Department of Gastroenterology, St Vincent's Hospital, Melbourne, Victoria 3065, Australia.
authors.forename: Alex
authors.initials: A
authors.lastname: Thompson
authors.affiliation: Centre for Population Health, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia; Infectious Diseases Unit, The Alfred Hospital, 55 Commercial Road, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventative Medicine, Monash University, 89 Commercial Road, Melbourne, Victoria 3004, Australia; Centre for Research Excellence in Injecting Drug Use, Burnet Institute, 85 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Joe
authors.initials: J
authors.lastname: Doyle
authors.affiliation: Melbourne School of Psychological Sciences, University of Melbourne, Victoria 3010, Australia.
authors.forename: Pip
authors.initials: P
authors.lastname: Pattison
authors.affiliation: Melbourne School of Psychological Sciences, University of Melbourne, Victoria 3010, Australia.
authors.forename: Garry
authors.initials: G
authors.lastname: Robins
mesh_terms: D000998:Antiviral Agents / Q000627:therapeutic use; D015897:Comorbidity; D003198:Computer Simulation; D006526:Hepatitis C / Q000188:drug therapy* / Q000453:epidemiology / Q000517:prevention & control / Q000635:transmission*; D006801:Humans; D015994:Incidence; D008962:Models, Theoretical; D015995:Prevalence; D012944:Social Support; D015819:Substance Abuse, Intravenous / Q000453:epidemiology*; D014739:Victoria / Q000453:epidemiology
chemical_list: D000998:Antiviral Agents
keywords: Hepatitis C; Injecting drug use; Injecting network; People who inject drugs; Social network