The relationship between age and risky injecting behaviours among a sample of Australian people who inject drugs

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 riskyinjecting behaviours.Methods: Data were taken from 11 years of a repeat cross-sectional study of sentinel samples of regularPWID (The Australian Illicit Drug Reporting System, 2001–2011). Multivariable Poisson regression wasused to explore the relationship between age and four outcomes of interest: last drug injection occurredin 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, interquar-tile range [IQR]: 27–40; median duration of injecting: 13 years [IQR: 7–20]). After adjusting for factorsincluding duration of injecting, each five year increase in age was associated with significant reductions inpublic injecting (adjusted incidence rate ratio [AIRR]: 0.90, 95% confidence interval [CI]: 0.88–0.92), nee-dle 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 inage 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 youngerPWID. Although they make up a small proportion of the current PWID population, younger PWID remainan important group for prevention and harm reduction.