Bridging supply and demand: relationship between cocaine seizures and prevalence estimates of consumption.

Objectives: Drug supply and demand indicators have been mainly analyzed on separate tracks without triangulating information on environmental drug availability and consumption. This study proposes an approach to jointly analyze prevalence of illicit drug consumption and indirect indicators of drug supply. Study design: This is an ecological study that correlates cocaine seizure data and consumption prevalence estimates at local level by considering Italian provinces as unit of analysis. Methods: The amount of seized cocaine in proportion to the number of potential consumers was computed at Italian provincial level from the 2005 database of the Italian Central Directorate for Anti-Drug Services (DCSA). Indicators of consumption prevalence, at provincial level, in 15-16 year-old students from the 2005 European School Survey Project on Alcohol and Other Drugs (ESPAD) and 15-54 old respondents from the 2005 Italian Population Survey on Alcohol and Drugs (IPSAD) were correlated with population-adjusted seizure total and with amounts of cocaine seized in smaller or larger seizures. ESPAD data were also regressed on seizure data after controlling statistically for the prediction accrued by socio-economic variables that might cause a covariation of seizure and consumption prevalence data. Regression-predicted prevalence values were computed and correlated to the ESPAD prevalence data of the following year. Results: There was a weak general correlation of population-adjusted seizure total and IPSAD, but not ESPAD prevalence indicators. In contrast, ESPAD data were more strongly correlated to small size seizures. The regression model yielded significant percentages of variance of prevalence data (18% and 23% in small and large provinces, respectively) explained by small size seizures also after removing the percentage of variance explained by socio-economic factors and particularly by the education level. A moderate correlation was found between seizure-based predicted values of consumption prevalence and ESPAD values of the following year. Conclusions: Associating adolescents’ prevalence estimates and cocaine seizure data at local level after ‘purifying’ them from trafficking- and wholesale-related large seizures may represent a starting point for a geo-referenced, seizure-based analysis of initiation into cocaine consumption. This approach may support the collaboration between enforcement and health systems, helping establish empirical regularities to be translated into useful information for local planners of drug prevention policies in areas more at risk of increasing incidence.