European Network to Develop Policy Relevant Models and Socio-Economic Analyses of Drug Use, Consequences and Interventions Final report: Part 4 – Time trends and incidence of problem drug use

Summary 
In the 1st 12-month period Kaplan Meyer and Cox Regression models were used to estimate the latency time between first drug use and first treatment. The group applied a Back-Calculation Model to estimate the incidence of problem drug use from the observed incidence in treatment, using the latency time. Latency time was remarkably similar in Amsterdam, London and Rome (on average between 6 and 8 years). However, this depended strongly on age at first drug use, latency time being longer in drug users who started at a younger age. This has important consequences for treatment centres, which might not be reaching young drug users sufficiently. Incidence curves were also estimated in the three cities on the basis of treatment data, using an updated version of the Empirical Bayesian Back Calculation procedure, showing important differences in the dynamic of the drug use epidemic. Data for Lisbon were analysed as well and showed similar results, despite being not from drugs treatment but from other services and therefore difficult to compare. This report is one of the outputs of a project funded by the European Commission, DG Research, Targeted Socio- Economic Resarch (TSER). Project no: ERB 4141 PL 980030, Contract no: SOE2-CT98- 3075 (Starting date: 1st December 1998 Duration: 36 months).  Links to all seven parts of the report are available below: Part 1: Overview Part 2 National Level Prevalence Estimation  Part 3 Local Level Prevalence Estimation Part 4 Modelling Time trends and Incidence Part 5 Modelling Geographic Spread withGeographic Information Systems (GIS)  Part 6 Modelling Costs and Cost-effectiveness of Interventions Part 7 Modelling Drug Markets and Policy options

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Abstract

This abstract is provided here as a convenience only. Check the publisher's website (if available) for the definitive version.

In the 1st 12-month period Kaplan Meyer and Cox Regression models were used to estimate the latency time between first drug use and first treatment. The group applied a Back-Calculation Model to estimate the incidence of problem drug use from the observed incidence in treatment, using the latency time. Latency time was remarkably similar in Amsterdam, London and Rome (on average between 6 and 8 years). However, this depended strongly on age at first drug use, latency time being longer in drug users who started at a younger age. This has important consequences for treatment centres, which might not be reaching young drug users sufficiently. Incidence curves were also estimated in the three cities on the basis of treatment data, using an updated version of the Empirical Bayesian Back Calculation procedure, showing important differences in the dynamic of the drug use epidemic. Data for Lisbon were analysed as well and showed similar results, despite being not from drugs treatment but from other services and therefore difficult to compare.

In the 2nd 12-month period Kaplan Meyer and Cox Regression models were used to estimate the latency time between first drug use and first treatment introducing epidemiological information about the phase of the sub-epidemics concerning the sub-groups defined by discrete covariates (ethnicity, gender, route...) in order to correct possible biases due to the different starting point of the sub-epidemics. The group generalised the Empirical Bayesian a Back-Calculation Model to estimate the incidence of problem drug use from the observed incidence in treatment, using the latency time as incubation distribution. User friendly interfaces were produced for the BC procedure written in S+ language. Latency time was remarkably similar in Amsterdam, London and Rome (on average between 6 and 8 years). However, this depended strongly on age at first drug use, latency time being longer in drug users who started at a younger age. Incidence curves were estimated for London, Amsterdam and Italy, showing important differences in the dynamic of the drug use epidemic. For Italy it was also possible to estimate some incidence curves at local (regional level). Data for Lisbon were analysed as well and showed similar results, despite being not from drugs treatment but from other services and therefore more difficult to compare. The incidence curve for Lisbon was estimated using a special snapshot method, namely the onset delay adjustment method (ODAM). Recent work from Dublin indicates that the situation might be very different, latency time on average about 2 years and not related to age at first use.

This might however be related to the stage of the drugs epidemic, which appears to be still in its early phase in Dublin, while already endemic in most other European cities. Unfortunately data from Dublin presently comprises only one year of treatment, thus it is not possible to check for the phase of the epidemic. Data from the French Community of Belgium were also analysed estimating the latency period with results comparable to the other sites (except Dublin). The incidence curve was estimated by the ODAM model. Similarly data from Budapest were also analysed producing results similar to those of Dublin. In this latter case, however, the phase of the epidemic could be considered due to the completeness of the data-set, which comprises more years of treatment. During the period 4 papers were written to be submitted to International Journals (2 of them are in press on UN Bulletin on Narcotics). Other papers related to the local analyses, results and policy implications were also produced. Preprints related to 3 of the 4 International papers can be presently downloaded from the website: http://mat.uniroma2.it/biometria/. A system dynamic model was developed and used to make some preliminary scenario analyses.

A structural equation model was also developed to evaluate prevention interventions, some very preliminary analyses were performed. The results were also presented at national and International meetings, such as, for example, the Harm Reduction Conference held in Jersey and the Workshop on “Dynamic drug policy: Understanding and controlling drug epidemics”, held in Vienna.

In the 3rd 12th month period the work was concentrated mostly on methodological developments and in summarizing all the results obtained in form of guidelines. Further local analyses were performed in order to obtain better estimates of the latency time distribution. Unfortunately new high quality local data are available for Italy only from the VE.de.TTE (Evaluation of Efficacy of Treatments for Heroin Addiction) multi-regional study carried out between 1998 and 1999 from ASP Lazio in different Italian regions, no further data were provided by the other partners. The group used again the Empirical Bayesian a Back-Calculation Model to estimate the incidence of problem drug use from the observed incidence in treatment, using the latency time as incubation distribution. Incidence curves were estimated for various areas in Italy (regional level). Further analyses considered regional aggregates obtained by spatial analysis and geographical aggregation. The incidence curves obtained for the aggregates show higher regularity and lower uncertainties due to increased sample sizes. A paper presenting the methods and analyses has been submitted.

The system dynamic model already developed was studied in depth both from a qualitative point of view and from a numerical point of view by means of a simulation procedure developed using the language S-plus. Several scenarios were obtained. A paper presenting both analyses has been submitted. A structural equation model was also developed to evaluate prevention interventions, some analyses were performed on the basis of a large data set coming from 35,000 interviews to military conscripts in Italy. Such analyses permitted to identify 4 different causal models for 4 different primary use substances. Work is in progress to write a paper summarising the results. On the basis of the preliminary analysis a new survey among military conscript in Italy has been designed in order to analyse time trends. The study will be developed in the next three years. Some of the various results obtained were presented at national and International meetings, such as, for example, the Harm Reduction Conference held in New Delhi. Further methodological developments allow to obtain correction of biases due to truncation in the estimates of the latency period. The experimental work performed within the project and the results obtained allow to set up a preliminary draft of guidelines.

Additional information 

This report (Part 4 – Time trends and incidence) was prepared by: Carla Rossi (Work Group coordinator)

Work Group members Time trends and incidence:
Erik van Ameijden , Anna Maria Bargagli, Massimiliano Bultrini, Marcel Buster , Maria Grazia Calvani, Catherine Comiskey , Simon Heisterkamp , Matthew Hickman , Alessandra Nardi, Lucilla Ravà, Jorge Ribeiro, Francis Sartor, Katalin Veress, Denise Walckiers .

Full Network Details:

Project Partners (project and work group coordinators):
Lucas Wiessing, EMCDDA (project coordinator), Gordon Hay, Univ. Glasgow, Carla Rossi, Lucilla Ravà, Univ. Rome ‘Tor Vergata’, Martin Frischer, Heath Heatlie, Univ. Keele, Hans Jager, Wien Limburg, RIVM, Christine Godfrey, Univ. York, Chloé Carpentier, Monika Blum, Kajsa Mickelsson, Richard Hartnoll, EMCDDA

The important input of all network participants and invited experts is fully acknowledged. For a list of network participants per working group and email contacts see Final Report Part 1, Annex A.

Other Network Participants and Invited Experts:
Fernando Antoñanzas, Rita Augustin, Marcel Buster, Maria Fe Caces, John Carnavale, Gloria Crispino O’Connell, Antonia Domingo, Ken Field, Gerald Foster, Maria Gannon, David Goldberg, Peter Hanisch, Toon van der Heijden, Matthew Hickman, Neil Hunt, Claude Jeanrenaud, Pierre Kopp, Petra Kümmler, Mirjam Kretzschmar, Marita van de Laar, Nacer Lalam, Fabio Mariani, Linda Nicholls, Alojz Nociar, Deborah Olzewski, Laetitia Paoli, Paivi Partanen, Paulo Penna, Harold Pollack, Maarten Postma, Thierry Poynard, Jorge Ribeiro, Janusz Sieroslawski, Ronald Simeone, Filip Smit, Juan Tecco, Jaap Toet, Gernot Tragler, Giovanni Trovato, Alfred Uhl, Julián Vicente, Katalin Veress, Denise Walckiers, Robert Welte, Ardine de Wit, John Wong, Tomas Zabransky, Terry Zobeck, Brigitta Zuiderma-van Gerwen.

Project funded by the European Commission, DG Research, Targeted Socio-Economic Resarch (TSER). Project no: ERB 4141 PL 980030, Contract no: SOE2-CT98-3075 Starting date: 1st December 1998
Duration: 36 months

Date of issue of this report: 31st January 2002

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Organisation (author) 
EMCDDA
Date 31 January 2002
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Authors 
Carla Rossi (Work Group coordinator) Work Group members Time trends and incidence: Erik van Ameijden , Anna Maria Bargagli, Massimiliano Bultrini, Marcel Buster , Maria Grazia Calvani, Catherine Comiskey , Simon Heisterkamp , Matthew Hickman , Alessandra Nardi, Lucilla Ravà, Jorge Ribeiro, Francis Sartor, Katalin Veress, Denise Walckiers .
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