Prevalence of injecting and non-injecting high-risk opioid use in Switzerland over more than two decades: understanding associations with opioid agonist treatment and needle and syringe programs

Thursday, 24 October, 2019 - 11:00 to 11:15
Insights zone 1 (I1)

Abstract

Background: Opioid agonist therapy (OAT) can reduce mortality and crime in high-risk opioid users (HROU). Both OAT and needle and syringe programs (NSP) can reduce risk of HIV and HCV infection in people who inject drugs (PWID). However, knowledge about the implementation of these measures is often insufficient or outdated. OAT coverage (proportion of HROU and PWID attending OAT in a given year) as well as NSP coverage (number of syringes provided per patient per year) are often unknown because prevalence estimates that form the denominators are not available.

Aims: To estimate HROU and PWID prevalence, OAT and NSP coverage for PWIDs in Switzerland between 1992 and 2020 by modeling relevant processes.

Methods: We applied a refined version of the lag-time distribution method (Nordt & Stohler 2006) using data from the OAT and heroin-assisted treatment (HAT) registers 1992-2015 of the canton of Zurich, Switzerland. An average of 3826 patients per year received OAT or HAT for at least one day between 1992 and 2015 (91 823 data points from 12 007 patients). Frequency of heroin/cocaine use and route of application came from entry, follow-up and cessation forms (126 894 data points from 9351 patients between 1997 and 2017). Annual number of syringes distributed to PWID were derived from pharmacies and low-threshold facilities in Switzerland between 1993 and 2015 (Lociciro et al. 2017).

Results: HROU prevalence peaked in 1997 at 35 767 persons (95% CI 32 576-39 153) and decreased afterwards to 21 656 (95% CI 19 735-23 685) in 2020. OAT coverage by age group was stable between 1992 and 2015: e.g. 34.2% (95% CI 30.7-37.8) for age 20, 65.1% (95% CI 60.8-69.5) for age 40, 70.0% (95% CI 63.6-76.3) for age 60. HROU in OAT increased from 15 104 (95% CI 13 441-16 871) in 1992 to 19 546 (95% CI 17 400-21 810) in 2003, then declining to 14 406 (95% CI 12 729-16 176) in 2020. PWID prevalence decreased from 24 433 (95% CI 21 459- 27 518) in 1992 to 3 925 (95% CI 2 974-5 005) in 2020. The proportion of HROU in OAT using heroin/cocaine declined form about 85% in 1992 to about 30% in 2020. The proportion of injecting among HROU in OAT who still used heroin/cocaine declined from about 75% in 1992 to about 25% in 2020. Injection use among HROU not in OAT also decreased from about 85% in 1992 to 40% in 2020. OAT coverage of HROU increased from 45.8% (95% CI 43.3-48.3) in 1992 to 66.5% (95% CI 62.0-71.0) in 2020. In contrast OAT coverage of PWID decreased from 38.7% (95% CI 35.6-41.9%) in 1992 to 26.9% (95% CI 20.9-33.5) in 2020. Although the number of syringes distributed declined from 6.4 million in 1993 to 2.2 million in 2015 the number of syringes per PWID per year increased from 266 (95% CI 235-303) in 1993 to 420 (95% CI 341-524) in 2015.

Key conclusion: The increase in OAT coverage for HROU between 1992 and 2015 was an effect of an aging HROU population, and not due to enhanced accessibility of services. The decline of PWID prevalence is driven mainly by three processes, (1) a general time trend decline of injecting drug use, (2) a strong decline of HROU who using heroin/cocaine in OAT, and (3) a lower probability of injecting among those who consumed less frequent heroin/cocaine in OAT. In line with this process we found that OAT coverage of PWIDs declined between 1992 and 2020 and was substantially lower than OAT coverage for HROU in general. In contrast, the NSP coverage in Switzerland increased between 1993 and 2015 on a high level compared to other countries.

Speakers

Presentation files

24 109 1100 Carlos Nordt .pdf465.54 KBDownload

Type

Keywords

Part of session