Evaluating the potential of wastewater-based epidemiology to estimate the retail illicit drug market size in Europe: A case study

Abstract

Background and aims

Estimating the retail drug market size is complex due to its clandestine nature, yet useful for intervention and policy planning. Wastewater-based epidemiology (WBE) offers an alternative strategy to estimate population-wide consumption trends by analysing influent wastewater, avoiding self-reporting biases associated with other estimation techniques, e.g., consumption or expenditure-based models. This study evaluates the applicability of WBE for drug market size estimation.

Methods

Using WBE data the drug market situation of amphetamine, cocaine, MDMA, and methamphetamine is estimated in European cities (n=75) through combination with price/purity information (Statistical Bulletin) published by the European Union Drugs Agency. Market sizes were estimated at three levels: (L1) pure drug quantities, (L2) adulterated retail drugs quantities, and (L3) market value. Furthermore, yearly consumption estimates from the commonly applied consecutive seven-day sampling is compared to a randomised stratified sampling approach in Brussels, Belgium.

Results

Challenges include the availability and accuracy of price and purity data, which complicates cross-country comparisons and hinders the higher-levels calculations. Due to missing data, the market value (L3) could only be calculated for a limited number of cities, i.e., 39% (amphetamine), 39% (cocaine), 1% (MDMA), and 23% (methamphetamine). Furthermore, statistically significant differences were shown for amphetamine (up to 139% measurement error) and methamphetamine (up to 58% measurement error) between both sampling approaches.

Conclusions

Particularly at city level, WBE can complement traditional market size estimations, but significant uncertainties remain. Future research should expand one-week consecutive sampling to a randomised stratified sampling approach tailored to drug and location.