title: Geographic Differences in Temporal Incidence Trends of Hepatitis C Virus Infection Among People Who Inject Drugs: The InC3 Collaboration.
abstract: BACKGROUND
  We determined temporal trends (1985-2011) in hepatitis C virus (HCV) incidence and associated behavioral exposures for people who inject drugs (PWID) from the United States (Boston, Baltimore, and San Francisco), Canada (Montreal), the Netherlands (Amsterdam), and Australia (Sydney and Melbourne).
  
  
  METHODS
  Using population-based cohort data from HCV-negative PWID, we calculated overall and within-city HCV incidence trends, HCV rates by study enrollment period (1985-2011), and temporal trends in exposure behaviors. Poisson regression models estimated trends in HCV incidence over calendar-time. Survival models identified risk factors for HCV incidence across cities and estimated independent effects of city and calendar period on HCV infection risk.
  
  
  RESULTS
  Among 1391 initially HCV-negative participants followed prospectively (1644.5 person-years of observation [PYO]), 371 HCV incident infections resulted in an overall incidence of 22.6 per 100 PYO (95% confidence interval [CI], 20.4-25.0). Incidence was highest and remained elevated in Baltimore (32.6/100 PYO), San Francisco (24.7/100 PYO), and Montreal (23.5/100 PYO), lowest in Melbourne and Amsterdam (7.5/100 PYO and 13.1/100 PYO, respectively), and moderate (21.4/100 PYO) in Sydney. Higher rates of syringe and equipment sharing and lower prevalence of opioid agonist therapy were associated with HCV incidence in cities with the highest incidence. Risk for infection dropped by 18% for every 3-year increase in calendar-time (adjusted hazard ratio, 0.8 [95% CI, .8-.9]) in the multivariable model.
  
  
  CONCLUSIONS
  Differences in prevention strategies and injecting contexts may explain the ongoing high HCV incidence in these North American cities and emphasize the need for scale-up of opioid agonist therapy and increased coverage of needle and syringe programs in North America.
authors.affiliation: Department of Epidemiology and Biostatistics, University of California, San Francisco.
authors.forename: Meghan D
authors.initials: MD
authors.lastname: Morris
authors.affiliation: Department of Epidemiology and Biostatistics, University of California, San Francisco.
authors.forename: Stephen
authors.initials: S
authors.lastname: Shiboski
authors.affiliation: Centre Hospitalier de l'Universite de Montreal (CRCHUM), Université de Montréal, Quebec, Canada.
authors.forename: Julie
authors.initials: J
authors.lastname: Bruneau
authors.affiliation: Department of Medicine, University of California, San Francisco.
authors.forename: Judith A
authors.initials: JA
authors.lastname: Hahn
authors.affiliation: Burnet Institute, Melbourne, Australia.
authors.forename: Margaret
authors.initials: M
authors.lastname: Hellard
authors.affiliation: Department of Public Health and Epidemiology of Infectious Disease, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Maria
authors.initials: M
authors.lastname: Prins
authors.affiliation: Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Cox
authors.affiliation: Kirby Institute, University of New South Wales, Sydney, Australia.
authors.forename: Gregory
authors.initials: G
authors.lastname: Dore
authors.affiliation: Kirby Institute, University of New South Wales, Sydney, Australia.
authors.forename: Jason
authors.initials: J
authors.lastname: Grebely
authors.affiliation: Department of Medicine, Massachusetts General Hospital, Boston.
authors.forename: Arthur Y
authors.initials: AY
authors.lastname: Kim
authors.affiliation: Department of Medicine, Massachusetts General Hospital, Boston.
authors.forename: Georg M
authors.initials: GM
authors.lastname: Lauer
authors.affiliation: Kirby Institute, University of New South Wales, Sydney, Australia.|School of Medical Sciences, University of New South Wales, Sydney, Australia; and.
authors.forename: Andrew
authors.initials: A
authors.lastname: Lloyd
authors.affiliation: Department of Epidemiology and Biostatistics, University of California, San Francisco.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rice
authors.affiliation: Centre Hospitalier de l'Universite de Montreal (CRCHUM), Université de Montréal, Quebec, Canada.
authors.forename: Naglaa
authors.initials: N
authors.lastname: Shoukry
authors.affiliation: Kirby Institute, University of New South Wales, Sydney, Australia.
authors.forename: Lisa
authors.initials: L
authors.lastname: Maher
authors.affiliation: Department of Internal Medicine, University of New Mexico Health Center, Albuquerque.
authors.forename: Kimberly
authors.initials: K
authors.lastname: Page
mesh_terms: D000328:Adult; D015331:Cohort Studies; D055030:Drug Users / Q000706:statistics & numerical data*; D005260:Female; D016174:Hepacivirus / Q000235:genetics; D006526:Hepatitis C / Q000453:epidemiology* / Q000635:transmission* / Q000821:virology; D006801:Humans; D015994:Incidence; D059012:Lost to Follow-Up; D008297:Male; D011159:Population Surveillance; D018570:Risk Assessment; D012307:Risk Factors; D062211:Spatio-Temporal Analysis; D055815:Young Adult
keywords: epidemiology; harm reduction strategies.; hepatitis C virus (HCV); incidence trends; people who inject drugs