Population surveys compared with wastewater analysis for monitoring illicit drug consumption in Italy in 2010–2014

Background: Monitoring consumption by population surveys (PS) is an important way to challenge the spread of illicit drugs (ID). To improve the information, we explored a complementary method, particularly wastewater analysis (WWA). Methods: We estimated the prevalence of use by PS, and the consumption by WWA, of cocaine, opioids, cannabis, methamphetamine and MDMA (ecstasy) from 2010 to 2014 in Italy and compared the results. Results: According to PS, cannabis and cocaine were the ID most used in Italy (last month prevalence 3.0% and 0.43% respectively in 2010) followed by opioids (0.17%) and amphetamines (0.14%). WWA gave similar findings, with cannabis consumption (4.35 g THC/day/1000 inhabitants) exceeding cocaine (0.78 g), heroin (0.092 g), methamphetamine and MDMA (0.103 g). The time trend investigated by PS showed significant decreases for all ID from 2010 to 2012. WWA also indicated a reduction of consumption for methamphetamine (p < 0.0001) and heroin (p < 0.01). Both methods showed an increase for cannabis in 2014 (p < 0.001) with the other ID unchanged. Spatial investigations by WWA showed that cannabis and cocaine were consumed significantly more in central Italy than in the north and south. PS indicated the same but only for cannabis. WWA was helpful to study weekly patterns of consumption, showing increases in cocaine and MDMA at weekends. Conclusions: PS and WWA were confirmed as complementary methods and when used together improved the information on ID use in Italy. We suggest that the combined use of the two approaches can give better information on ID use in the population.