Elsevier

Drug and Alcohol Dependence

Volume 158, 1 January 2016, Pages 177-180
Drug and Alcohol Dependence

Short communication
From initiating injecting drug use to regular injecting: Retrospective survival analysis of injecting progression within a sample of people who inject drugs regularly

https://doi.org/10.1016/j.drugalcdep.2015.11.022Get rights and content

Highlights

  • Progression from the initiation of injecting drug use to regular injecting is rapid.

  • Half the sample made this progression within 1 year post-initiation.

  • 91% of the sample had made the progression by the fourth year.

  • Initiation with heroin was found to be associated with a more rapid progression.

Abstract

Background

The initiation of injecting drug use and the commencement of a pattern of regular injecting are key milestones in injecting careers. The progression from initiation to regular injecting is a poorly understood period in these careers.

Methods

Cross-sectional baseline data from a sample of people who inject drugs regularly (N = 691), recorded the age at which participants initiated injecting drug use and the age they became regular (at least once per month) injectors. Survival analysis compared the rapidity of progression to regular injecting across sub-groups within the sample using bivariate log-rank testing and multivariable Cox regression.

Results

Half of all participants progressed to regular injecting within 1 year of initiation and by the fourth year post-initiation, 91% had progressed. In bivariate analysis, there were significant differences in equality of hazards by sex (X2 = 7.75, p < 0.01), from whom participants learnt to inject (X2 = 22.32, p < 0.01) and the drug of injection initiation (X2 = 18.36; p < 0.01). In the multivariable Cox model, only initiating injecting with heroin (HR = 1.28; 95% CI: 1.09–1.50) compared with other drugs (predominantly methamphetamine) showed a significantly greater hazard, suggesting a faster progression to regular injecting.

Conclusion

This study showed that among our sample of eventual regular injectors, progression from initiation to regular injecting was rapid. By gaining a greater understanding of the dynamics of this progression, the ability to appropriately target interventions and future research is subsequently informed.

Introduction

The natural history of the injecting careers of people who inject drugs (PWID) contains periods of heightened risk and harm (Huo et al., 2006). For example, the period following initiation of injecting drug use has been shown to be a period of heightened risk, with a substantial proportion of blood-borne virus (BBV) infections amongst PWID occurring within the first years after initiation (Bulled and Singer, 2011, Hagan et al., 2008, Maher et al., 2006, Miller et al., 2003, Stoove et al., 2008) As careers progress other risks are heightened, such as the risk of overdose, which has been shown to be highest amongst older, more experienced PWID (Dietze et al., 2006, Mcgregor et al., 2001). There are, however, considerable individual differences in natural histories; for example, although many PWID initiate injecting in late adolescence or early adulthood (Day et al., 2005, Huo et al., 2006), others initiate when substantially older (Carneiro et al., 1999).

The initiation of injecting drug use and the commencement of a pattern of regular injecting are milestones in injecting careers. Extensive literature examines both initiation (Day et al., 2005, Van Ameijden et al., 1994, Werb et al., 2013) and entrenched injecting drug use (Chitwood et al., 2001, Des Jarlais et al., 2007, Horyniak et al., 2013, Miller et al., 2003), but we could find no studies exploring the temporal characteristics of injecting progression. Lai et al. (2000) showed that the time from first use of heroin to first injection of heroin was a median 11 months for males and 22 months for females, whilst Lee et al. (2012) showed that the average time from first methamphetamine use to regular methamphetamine use was 2 years. However, neither of these studies analysed progression from injecting initiation through to regular injecting.

Unlike other chronic health problems, the progression of injecting drug use is not well understood (Hickman et al., 2012). The gap highlighted here has implications for the targeting of public health interventions for newly initiated PWID. Improved knowledge of progression would allow risk reduction interventions to be tailored towards the transitional phase between initiation and regular injecting, just as interventions have been designed to prevent the transition from non-injecting to injecting drug use (Werb et al., 2013).

This paper presents an examination of cross-sectional data from a sample of people who inject drugs regularly, to retrospectively examine the rapidity of progression from initiation to regular injecting drug use and how this varies across different sub-groups. Evidence suggests that age (Miller et al., 2006), sex (Martin, 2010), ethnicity (Day et al., 2005), social networks (Day et al., 2005) and the influence of initiators (Bryant and Treloar, 2008) affect the dynamics of injecting initiation. We analysed these and other exposures and their influence upon the rapidity of progression from initiation to regular injecting drug use.

Section snippets

Recruitment

Baseline data were obtained from the Melbourne injecting drug user cohort study (MIX), which was designed to examine trajectories of injecting drug use. MIX began in Melbourne, Australia in 2008 and is described in detail elsewhere (Horyniak et al., 2013). Our analysis includes the original MIX participants (N = 688) along with an additional 69 participants enrolled into the study in 2011 via past involvement in the Networks II cohort (commenced in 2005; Sacks-Davis et al., 2012). Eligibility

Demographics

Of the 691 participants included in analysis, 66% were male, 79% Australian-born and 6% identified as Indigenous. Mean age at baseline interview was 27 years.

Time to regular injecting

The range of reported ages at first injection was 8–30 years (median 17, IQR 15–19). The range of ages at commencement of regular injecting was 10–38 years (median 18, IQR 16–21). The range of time progression to regular injecting was 1–15 years. Half of all participants (49%) progressed to regular injecting within 1 year of initiation. A

Findings

Our study suggests that progression to regular injecting within our sample of eventual regular injectors occurred relatively quickly, with nearly half of the sample progressing to regular injecting within a year of initiation, and over 90% progressing within 4 years.

After controlling for other variables, we found the only significant result was the initiation of injecting drug use with heroin over other drug types (primarily methamphetamine), with a resulting greater level of hazard. Previous

Conclusion

This study showed that progression from initiation to regular injecting was relatively rapid in our sample of long-term, regular injectors. Although the sole significant association with progression in multivariable analysis was initiation with heroin (over other drugs), the finding of rapid progression to regular injecting is important. By gaining a better understanding of the dynamics of injecting progression amongst regular injectors our ability to appropriately target interventions and

Contributors

DO’K led the analysis and writing of the article. DH and PD assisted with conceptualisation and provided essential input and support during analysis and writing. All authors have read the article and approve of its submission to Drug and Alcohol Dependence.

Role of funding source

The MIX study was funded by The Colonial Foundation Trust and the National Health and Medical Research Council (NHMRC Grant no. 545891). DO’K receives support from the NHMRC through a postgraduate scholarship. DH is an NHMRC Early Career Fellow. PD is an NHMRC Senior Research Fellow. The authors gratefully acknowledge the contribution to this work of the Victorian Operational Infrastructure Support Program's support of the Burnet Institute. The funding bodies played no role in the study design,

Conflict of interest

PD has received funding from Gilead Sciences Inc and Reckitt Benckiser for work unrelated to this study.

Acknowledgements

The authors wish to thank the participants of the MIX study along with the staff of the community-based organizations who assisted with recruitment. Thank you to members of the MIX study team who assisted with participant recruitment, follow up and interviewing.

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