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Background Estimations of drug use are mostly based on population surveys that can suffer from response biases. The current study evaluates using wastewater-based epidemiology (WBE) for assessing illicit drug use by comparing wastewater data with that from a population survey. Methods Introductory letters (29,083) were sent to inhabitants of Lier, Belgium, asking them to participate in an online survey study. Participants were asked to indicate their drug use in the past week for a 12-week period (September–November 2014). Concomitant wastewater samples were collected from the associated wastewater treatment plant in four bi-weekly periods. Samples were analyzed using solid-phase extraction and liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). Results On average, 263 (1%) inhabitants filled out the questionnaire each week. According to the survey results, cannabis was the most used drug, followed by amphetamine, cocaine and methylenedioxymethamphetamine (MDMA). Wastewater data corroborated these results. Cocaine, amphetamine and MDMA showed a significant difference between days of the week. The four sampling periods differed significantly from each other for cocaine, amphetamine and methadone. Conclusion Observed drug consumption patterns from survey and wastewater data match national and international data. Wastewater analyses confirm that WBE can be reliably used to confirm patterns and trends in drug use. Future studies should focus on identifying the most opportune sampling period giving the most reliable estimates of drug use and use smaller, contained communities such as festivals or prisons if methodology allows.

Background/aims: Alcohol and nicotine are the two most used substances world-wide and associated with increased burden of disease. Since surveys on substance use may be difficult due to response biases, wastewater-based epidemiology (WBE) was developed as a more objective measure of nicotine and alcohol use. This study compares estimates of nicotine and alcohol use from a wastewater sampling campaign in a medium-sized Belgian city with a concurrently executed population survey. Methods: 29,083 letters about participation in an online survey study on weekly alcohol and tobacco use were sent to the inhabitants of Lier, Belgium. Wastewater samples were collected from the associated treatment plant in four bi-weekly periods. Samples were analyzed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Ethylsulfate was used as alcohol biomarker and cotinine and trans-3'-hydroxycotinine as nicotine biomarker. Results: 263 (1%) surveys were filled out on average per week. According to survey data, alcohol and nicotine were used less than in the rest of Belgium and this was matched by the wastewater data. Nicotine use, but not alcohol use, showed a significant variation over the sampling periods. Both nicotine and alcohol showed increase use during the weekend while only alcohol showed a different use pattern throughout the week. Conclusion: No correlation between WBE and survey data could be demonstrated, possibly due to small sample sizes. However, this study shows that weekly trends in alcohol and nicotine use can be quickly detected from wastewater analysis and the occurrence of major events such as festivals can be identified.