title: The relationship between age and risky injecting behaviours among a sample of Australian people who inject drugs.
abstract: BACKGROUND
  Limited evidence suggests that younger people who inject drugs (PWID) engage in high-risk injecting behaviours. This study aims to better understand the relationships between age and risky injecting behaviours.
  
  
  METHODS
  Data were taken from 11 years of a repeat cross-sectional study of sentinel samples of regular PWID (The Australian Illicit Drug Reporting System, 2001-2011). Multivariable Poisson regression was used to explore the relationship between age and four outcomes of interest: last drug injection occurred in public, receptive needle sharing (past month), experiencing injecting-related problems (e.g. abscess, dirty hit; past month), and non-fatal heroin overdose (past six months).
  
  
  RESULTS
  Data from 6795 first-time study participants were analysed (median age: 33 years, interquartile range [IQR]: 27-40; median duration of injecting: 13 years [IQR: 7-20]). After adjusting for factors including duration of injecting, each five year increase in age was associated with significant reductions in public injecting (adjusted incidence rate ratio [AIRR]: 0.90, 95% confidence interval [CI]: 0.88-0.92), needle sharing (AIRR: 0.84, 95% CI: 0.79-0.89) and injecting-related problems (AIRR: 0.96, 95% CI: 0.95-0.97). Among those who had injected heroin in the six months preceding interview, each five year increase in age was associated with an average 10% reduction in the risk of heroin overdose (AIRR: 0.90, 95% CI: 0.85-0.96).
  
  
  CONCLUSIONS
  Older PWID report significantly lower levels of high-risk injecting practices than younger PWID. Although they make up a small proportion of the current PWID population, younger PWID remain an important group for prevention and harm reduction.
authors.affiliation: Centre for Population Health, Burnet Institute, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria 3004, Australia. Electronic address: danielle@burnet.edu.au.
authors.forename: D
authors.initials: D
authors.lastname: Horyniak
authors.forename: P
authors.initials: P
authors.lastname: Dietze
authors.forename: L
authors.initials: L
authors.lastname: Degenhardt
authors.forename: P
authors.initials: P
authors.lastname: Higgs
authors.forename: F
authors.initials: F
authors.lastname: McIlwraith
authors.forename: R
authors.initials: R
authors.lastname: Alati
authors.forename: R
authors.initials: R
authors.lastname: Bruno
authors.forename: S
authors.initials: S
authors.lastname: Lenton
authors.forename: L
authors.initials: L
authors.lastname: Burns
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001315:Australia / Q000453:epidemiology; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D012309:Risk-Taking; D015819:Substance Abuse, Intravenous / Q000175:diagnosis* / Q000453:epidemiology* / Q000523:psychology; D055815:Young Adult
keywords: Age; Australia; Injecting drug use; Injury; Overdose