Research paper
A decline in the prevalence of injecting drug users in Estonia, 2005–2009

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Abstract

Aims

Here we report a study aimed at estimating trends in the prevalence of injection drug use between 2005 and 2009 in Estonia.

Background

Descriptions of behavioural epidemics have received little attention compared with infectious disease epidemics in Eastern Europe.

Methods

The number of injection drug users (IDUs) aged 15–44 each year between 2005 and 2009 was estimated using capture–recapture methodology based on 4 data sources (2 treatment data bases: drug use and non-fatal overdose treatment; criminal justice (drug related offences) and mortality (injection drug use related deaths) data). Poisson log-linear regression models were applied to the matched data, with interactions between data sources fitted to replicate the dependencies between the data sources. Linear regression was used to estimate average change over time.

Results

There were 24305, 12,292, 238, 545 records and 8100, 1655, 155, 545 individual IDUs identified in the four capture sources (police, drug treatment, overdose, and death registry, accordingly) over the period 2005–2009. The estimated prevalence of IDUs among the population aged 15–44 declined from 2.7% (1.8–7.9%) in 2005 to 2.0% (1.4–5.0%) in 2008, and 0.9% (0.7–1.7%) in 2009. Regression analysis indicated an average reduction of about 1600 injectors per year.

Conclusion

While the capture–recapture method has known limitations, the results are consistent with other data from Estonia. Identifying the drivers of change in the prevalence of injection drug use warrants further research.

Introduction

There is evidence that both risk behaviours (high risk sexual behaviour, illicit drug use) and related infectious diseases (sexually transmitted and blood borne infections) are constantly evolving in the interplay between social-environmental factors, pathogens and their hosts (Bello, Simwaka, Ndhlovu, Salaniponi, & Hallett, 2011). In an epidemic outbreak of an infectious disease the prevalence in a particular population does not grow indefinitely, but saturates at some level. Following the initial spread there is generally a fall in the incidence followed by a reduction in prevalence. The same is likely to apply to behavioral epidemics. There are similarities between the spread of drug use, in particular the spread of the use addictive drugs (such as heroin), and that of infectious diseases. The use of drugs is communicated, not as an organic agent, but as a kind of “innovative” social practice or custom, and not to everyone but only to those who, for whatever reason, are not immune (i.e., susceptible individuals) (Rossi, 2002).

Behavioural epidemics have received little attention compared with infectious disease epidemics in Eastern Europe.

Estonia is a small country in the northern–eastern part of Europe with a population of about 1,340,000 (Statistics Estonia, 2012). According to a global review of injection drug use and HIV epidemiology, Estonia has one of the highest prevalences of injection drug users (IDUs) among people aged 15–64 years (1.51% in 2007) coupled with a high HIV prevalence among IDUs (Mathers et al., 2008, Uusküla et al., 2008). We have previously estimated the prevalence of IDU among ages 15–44 in Estonia to be 2.4% in 2004 (Uusküla et al., 2007).

Capture–recapture (CRC) is an indirect method that estimates population size from the degree of overlap between two or more separate samples from a population (Hook & Regal, 1995). The method calculates the extent to which the same individuals appear in datasets from different sources, and extrapolates from this to estimate the number of individuals who do not appear in any of the sources. Several assumptions are made when using CRC: the population is closed; overlaps between datasets can accurately be identified; the samples are independent or multiple sources are used to account for dependencies; all members of the population have an equal probability of occurring in any of the sources; representative samples of the population can be obtained (Millar, Domingo-Salvany, Eastwood, & Hay, 2008). As injection drug use encompasses criminal and health problems, CRC studies should obtain data from both criminal justice and healthcare sources to target the population (Hickman, Seaman, & de Angelis, 2001).

We have used CRC methodology to estimate the number of IDUs in the 15–44 year age range in Estonia for each year between 2005 and 2009and to examine the trend in prevalence of injection drug users during this period.

Section snippets

Data sources and definitions

Our target population was men and women aged 15–44 who were residents in Estonia and injecting drugs at some time between 2005 and 2009. Series of cross-sectional studies conducted in several location and across the period of 2004–2011 have documented that overwhelming majority (∼95%) of IDUs in Estonia are of age 15–44 (Talu et al., 2010, Uusküla et al., 2012). We used four data sources: (1) police data on drug-related offences, (2) data on drug treatment from the Estonian Health Insurance

Results

The four capture sources are described in Table 2. Gender was not recorded in 0.3% of records in the POLIS database, and these were therefore excluded from the analyses. In the other data sets, full identification was possible for all records. Comparison of the ID variable with the databases’ own ID code revealed that 19 persons in the police and 4 persons in the EHIF data set had identical characteristics to another person but the database's inner ID indicated that they were different persons.

Discussion

This is the first study from Eastern Europe designed to describe the course of the injection drug users epidemic. There was a reduction in the estimated number of injection drug users over time. An estimated number of the injection drug users in Estonia were 15,675, 11,493 and 5362 for the years 2005, 2008 and 2009, accordingly. These estimates translate as a prevalence of IDUs among the population aged 15–44 in Estonia 2.7% (1.8–7.9%) in 2005 to 2.0% (1.4–5.0%) in 2008, and 0.9% (0.7–1.7%) in

Conclusions

The costs that illicit drugs impose on society are high and illicit drug use is notoriously difficult to control (Room and Reuter, 2012, Ryan, 1998). Research into the course of drug use epidemics and their drivers are important contributors to the knowledge needed to develop effective control interventions and policies.

This study, estimating IDU prevalence using CRC methodology documented a decrease in IDU prevalence over a 5-year period in Estonia. While acknowledging the limitations of the

Acknowledgements

The study was supported by the grant SF0180060s09 from the Estonian Ministry of Education and Research; by the R01 AI 083035 grant from the NIH (USA); and the EMCDDA Grant No. GA.12.RTX.007.1.0.

We thank Senior Inspector Ain Borodin and Chief Superintendent of the Police Work Department, Analysis and Planning Division Marilis Sepp; Ms Triin Tõrvand from the Estonian Health Insurance Fund; and the Head of the Estonian Causes of Death Registry Gleb Denissov for their valuable contributions.

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