Mapping international drug use through wastewater-based epidemiology

Wastewater-based epidemiology is a rapidly developing scientific discipline with the potential for monitoring close to real-time, population-level trends in illicit drug use.

By sampling a known source of wastewater, such as a sewage influent to a wastewater treatment plant, scientists can estimate the quantity of drugs used in a community from the measured levels of illicit drugs and their metabolites excreted in urine.

In 2011, this method of collecting data on use of stimulants by urban populations using a common sampling protocol was applied for the first time by an international group of scientists, the SCORE group (Sewage analysis CORe group Europe, www.score-network.eu). Since then, SCORE has collected data every year with an ever increasing number of participating cities, including ones from outside Europe.

The results of the international monitoring campaigns performed over seven years (2011-2017) are now compiled in an article published in the prestigious journal Addiction (doi:10.1111/add.14767).

In total, wastewater from over 60 million people in 120 cities from 37 countries was analyzed at least once over a one-week period to explore spatial population-level trends in the use of four illicit substances (amphetamine, methamphetamine, ecstasy, cocaine). Twenty-six cities from 14 European countries (covering approx. 19.3 million people) were monitored for at least five years, building a core data set that allowed to asses temporal trends in drug-taking behaviours.

Differences in drug use across Europe

The findings confirm the wide spatial differences existing across Europe.

Cocaine dominates the drug use scenario in southern and western cities (in Switzerland, Italy, France, Spain, United Kingdom), and its levels underwent an upsurge over 2011-2017 in most of the sampled sites. Belgium and The Netherlands reported also a very high use of cocaine and of amphetamine, a substance that also increased its consumption in some northern European countries.

The consumption of methamphetamine, although low on average when compared to other stimulants, presented some localized hot-spots in eastern cities (in Slovakia, Czech Republic and east of Germany) and it is being expanded to the north and centre of Europe.

Ecstasy does not dominate any drug scenario, but its use was increased over the period 2011-2017 in most of the cities where it was reported. Unlike the European overview, methamphetamine dominated the drug landscape in cities monitored in North America (United States and Canada) and Australasia (Australia, New Zealand and South Korea), with average levels exceeding by far those found in eastern Europe. In South America (Colombia and Martinique) cocaine prevailed over the other three substances. No temporal trends could be discerned in this case due to the recent inclusion of non-European sites in the international monitoring campaigns.

The correspondence between drug use figures derived from wastewater analyses and from established epidemiological indicators, e.g. prevalence data or drug seizure statistics, demonstrates the potential of the analysis of wastewater as an additional and complementary indicator of drug-taking trends. This discipline provides near real-time, population-level trends in illicit drug consumption that allow to identify new patterns of abuse much earlier than other methodologies.

The correspondence between drug use figures derived from wastewater analyses and from established epidemiological indicators, e.g. prevalence data or drug seizure statistics, demonstrates the potential of the analysis of wastewater as an additional and complementary indicator of drug-taking trends. This discipline provides near real-time, population-level trends in illicit drug consumption that allow to identify new patterns of abuse much earlier than other methodologies.

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