The relationship between age and risky injecting behaviours among a sample of Australian people who inject drugs
Introduction
There is evidence to suggest that the population of people who inject drugs (PWID) in Australia is ageing; over the past decade significant increases in median age have been detected in repeat cross-sectional studies of Needle and Syringe Program (NSP) clients and community-recruited PWID (Iversen et al., 2011, Stafford and Burns, 2011). This may reflect the ageing general population, including early-onset substance users (European Monitoring Centre for Drugs and Drug Addiction, 2008, World Health Organisation, 2011), as well as reduced initiation to heroin injecting following a period of reduction in heroin supply in late 2000/early 2001, in what had been heroin-dominated illicit drug markets, particularly in the country's two most populous jurisdictions, New South Wales and Victoria (Topp et al., 2001, Degenhardt et al., 2004, Degenhardt et al., 2005, Day et al., 2006). Although there has been recent attention to ageing PWID in public health research, particularly in relation to hepatitis C virus (HCV) related morbidity (Higgs and Maher, 2010, Gibson et al., 2011), further research is required to understand the injecting behaviours and associated health needs of younger PWID.
Research into the influence of age on patterns of injecting drug use (IDU) and associated risk behaviours has shown that compared with their older counterparts, younger PWID (commonly defined as those below 30 years of age) report injecting drugs at a higher frequency (Miller et al., 2007, Degenhardt et al., 2008), higher levels of sharing of injecting equipment (Fennema et al., 1997, Kral et al., 2000, Miller et al., 2007, Degenhardt et al., 2008) and engaging in high-risk injecting practices, such as ‘backloading’ (a process in which one syringe is used to mix drugs and to give measured shares to other PWID by squirting the drug solution directly into their syringes; Kral et al., 2000). These behaviours have significant implications for the risk of blood-borne virus (BBV) acquisition, and vascular and tissue injuries, as well as prevention practices (Jose et al., 1993, Topp et al., 2008, Pouget et al., 2011). Younger PWID also report limited use of health and drug treatment services (Cronquist et al., 2001, Miller et al., 2007, Day et al., 2011). These studies however have tended to group participants into just two or three age categories (usually ≤25 years or ≤30 years compared with older PWID), thereby not considering the effects of age within these groups. Further, previous studies have not focused on age-related differences in health outcomes such as drug overdose or injecting-related injury.
Although younger PWID may make up a small proportion of the current PWID population, evidence of their high-risk injecting behaviours and poor service utilisation suggest that they are an important target population for harm reduction and drug treatment services. In this paper, we use 11 years of repeat cross-sectional surveys conducted among sentinel samples of regular Australian PWID to generate robust estimates of the associations between age and selected risky injecting behaviours and related health outcomes.
Section snippets
Study methods
Data were obtained from the Illicit Drug Reporting System (IDRS), which has been described in detail elsewhere (Hando et al., 1998). In brief, participants were recruited using convenience sampling through NSPs, treatment agencies, advertisements in street press and peer referral, in the capital cities of all Australian states and territories. Participants were eligible for the study if they: were aged 16 years or older, had injected drugs at least monthly in the six months preceding interview,
Results
The percentage of first-time participants in annual IDRS samples fluctuated over time, from 74% in 2002 to as low as 55% in 2010. In total, 6795 first-time study participants were included in analysis, representing 67% of the overall study population; the number of participants decreased from 951 in 2001 to 491 in 2011 (Supplementary Material, Table 1). Two thirds of participants were male (66%), and the majority spoke English as their main language (96%). The median age of participants was 33
Discussion
The results of this study of almost 7000 regular PWID suggest that age is related to the extent to which PWID engage in high-risk injecting behaviours and that this relationship has remained stable across the past decade.
Each five year increase in age was associated with significantly lower levels of high-risk injecting behaviours: an average 10% reduction in the likelihood of public injecting, and an average 16% reduction in the likelihood of receptive needle sharing. These associations
Role of funding source
The Illicit Drug Reporting System is funded by the Australian Government Department of Health and Ageing, and is coordinated by the National Drug and Alcohol Research Centre at the University of New South Wales. The authors gratefully acknowledge the contribution to this work of the Victorian Operational Infrastructure Support Program. DH is supported by an Australian Postgraduate Award, and receives additional funding through the Australian National Health & Medical Research Council (NHMRC)
Contributors
DH and PD developed the project concept and analysis plan; DH conducted analysis and wrote the initial draft of the manuscript. All other authors contributed to the analysis and interpretation of data, and approved the final manuscript.
Conflict of interest
No conflict declared.
Acknowledgements
The authors would like to acknowledge the study participants and the numerous researchers across Australia who assisted with study coordination and data collection. Thanks to Maelenn Gouillou, Tim Spelman and Paul Agius for assistance with statistical analysis.
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