An estimation of the prevalence of opioid dependence in New Zealand

Abstract 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 treatment 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.