title: Changes in blood-borne infection risk among injection drug users.
abstract: BACKGROUND
  Population-level hepatitis C virus (HCV) infection incidence is a surrogate for community drug-related risk.
  
  
  METHODS
  We characterized trends in human immunodeficiency virus (HIV) and HCV infection incidence and HCV infection prevalence among injection drug users (IDUs) recruited over 4 periods: 1988-1989, 1994-1995, 1998, and 2005-2008. We calculated HIV and HCV infection incidence within the first year of follow-up among IDUs whose test results were negative for these viruses at baseline (n = 2061 and n = 373, respectively). We used Poisson regression to compare trends across groups.
  
  
  RESULTS
  HIV infection incidence declined significantly from 5.5 cases/100 person-years (py) in the 1988-1989 group to 2.0 cases/100 py in the 1994-1995 group to 0 cases/100 py in the 1998 and 2005-2008 groups. Concurrently, HCV infection incidence declined but remained robust (22.0 cases/100 py in the 1988-1989 cohort to 17.2 cases/100 py in the 1994-1995 cohort, 17.9 cases/100 py in the 1998 cohort, and 7.8 cases/100 py in the 2005-2008 cohort; P = .07). Likewise, HCV infection prevalence declined, but chiefly in younger IDUs. For persons aged <39 years, relative to the 1988-1989 cohort, all groups exhibited significant declines (adjusted prevalence ratio [PR] for the 2005-08 cohort, .73; 95% confidence interval [CI], .65-.81). However, for persons aged ≥ 39 years, only the 2005-2008 cohort exhibited declining prevalence compared with the 1988-1989 cohort (adjusted PR, .87; 95% CI, .77-.99).
  
  
  CONCLUSIONS
  Although efforts to reduce blood-borne infection incidence have had impact, this work will need to be intensified for the most transmissible viruses, such as HCV.
authors.affiliation: Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA. shmehta@jhsph.edu
authors.forename: Shruti H
authors.initials: SH
authors.lastname: Mehta
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Astemborski
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Kirk
authors.forename: Steffanie A
authors.initials: SA
authors.lastname: Strathdee
authors.forename: Kenrad E
authors.initials: KE
authors.lastname: Nelson
authors.forename: David
authors.initials: D
authors.lastname: Vlahov
authors.forename: David L
authors.initials: DL
authors.lastname: Thomas
mesh_terms: D000328:Adult; D015142:Baltimore / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D015658:HIV Infections / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D016174:Hepacivirus / Q000302:isolation & purification; D006526:Hepatitis C / Q000097:blood / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012044:Regression Analysis; D012307:Risk Factors; D012309:Risk-Taking; D015819:Substance Abuse, Intravenous / Q000150:complications* / Q000453:epidemiology / Q000821:virology; D011795:Surveys and Questionnaires; D055815:Young Adult