International Journal of Drug Policy 23 (2012) 87–89 Contents lists available at ScienceDirect International Journal of Drug Policy jo ur n al homep age: www.elsevier.com/locate/drugpo Short report An estimation of the prevalence of opioid dependence in New Zealand Simon J. Adamson a,* , Daryle E.A. Deering a , J. Doug Sellman a , Janie Sheridan b , Charles Henderson c , Rhonda Robertson d , Sheridan Pooley d , Samadhi D. Campbell a , Chris M.A. Frampton e a National Addiction Centre (NAC), Department of Psychological Medicine, University of Otago, Christchurch, New Zealand b School of Pharmacy, University of Auckland, New Zealand c Needle Exchange Programme, New Zealand d ¯ Aotearoa Alcohol and Other Drug Consumer Network, New Zealand e Department of Psychological Medicine, University of Otago, Christchurch, New Zealand a r t i c l e i n f o Article history: Received 2 June 2010 Received in revised form 16 May 2011 Accepted 20 May 2011 Keywords: Opioid dependence Prevalence Multiplier method Treatment need a b s t r a c t Background: An accurate prevalence estimate for opioid dependence in New Zealand, and hence the extent of unmet treatment need, is lacking. Methods: Opioid users were recruited via snowball sampling, with participants initially recruited from opioid substitution treatment (OST) services and dedicated needle exchanges in Auckland, Tauranga and Christchurch. Participants estimated the number of people they knew personally who were receiving OST and who were not receiving OST, but were using opioids daily or almost daily. From these estimates a multiplier of the ratio between these two groups was derived and applied to the known number receiving OST in New Zealand to arrive at the total population estimate. Results: The mean multiplier estimate, weighted for treatment site, for 84 recruited participants was 2.015. The multiplier was higher for Christchurch. Initial recruitment source did not influence the value of the multiplier estimate. When the multiplier was applied to the known size of the New Zealand OST treat- ment population the total opioid dependent population was estimated to be 9142 (95% CI: 8248–10036), of whom half were not receiving OST. Conclusion: This figure was lower than for previous less robust estimates, but still represents a substantial level of unmet need. Greater effort needs to be made to close this treatment gap. © 2011 Elsevier B.V. All rights reserved. Introduction Opioid dependence is a significant mental health disorder, with a high death rate in the absence of treatment (Degenhardt, Hall, Lynskey, & Warner-Smith, 2004; Seaman, Brettle, & Gore, 1998). The United Nations estimated the annual prevalence of opioid use in 2007 as being 0.4% of the world’s population aged 15–64, ranging from 0.2% in Africa to 0.7% in Europe (United Nations Office on Drugs and Crime, 2009). Within any individual jurisdiction accurate estimations of prevalence are important for a variety of policy reasons. These include determining the appropriate mix of treatment and public health harm minimisation interventions, evaluating the success of interdiction, and the implications of any variation in regional and national prevalence rates over time. At present no accurate figure exists for the prevalence of opioid dependence in New Zealand. In * Corresponding author at: National Addiction Centre (NAC), Department of Psychological Medicine, University of Otago, Terrace House, P.O. Box 4345, Christchurch, New Zealand. Tel.: +64 3 3640480; fax: +64 3 3641225. E-mail address: simon.adamson@otago.ac.nz (S.J. Adamson). this paper we describe a new method for deriving such an estimate for New Zealand. Methods A snowballing technique was used to recruit an opioid depen- dent sample from which a multiplier estimate was derived. The “multiplier” estimate refers to an indirect method of estimating the population prevalence of a disorder based on two pieces of infor- mation: the known number of a defined subset of the population, in this case those receiving OST, and the ratio (the multiplier) of this subset to the total population in an identified sample (Law, Degenhardt, & McKetin, 2006). This method has been found to generate estimates comparable with other methods (Degenhardt, Rendle, Hall, Gilmour, & Law, 2004; Kraus et al., 2003). Three cities were selected, comprising the largest cities in both the North (Auckland) and South (Christchurch) Islands and a some- what smaller metropolitan area (Tauranga). The sample was recruited by snowballing initiated from OST services (four participants per city) and needle exchanges (eight per city), with eligibility being daily or almost daily users of opioids or currently receiving OST. Peer-led needle exchange programmes, as 0955-3959/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.drugpo.2011.05.013