Spatio-Temporal Surveillance of Drugs of Abuse and Novel Psychoactive Substances in Tunisian Wastewater: A Multi-City Study on Consumption Patterns and the Impact of COVID-19

Drugs of abuse (DAs) and novel psychoactive substances (NPS) are increasingly detected in urban wastewater, yet data from North Africa remain scarce. This study is the first to apply wastewater-based epidemiology (WBE) to assess drug consumption patterns across 15 wastewater treatment plants in six major Tunisian cities. Daily 24-hour composite samples were collected for seven consecutive days per site between November and December 2021. Samples were analyzed using liquid chromatography-tandem mass spectrometry to quantify 11 drugs and their metabolites. Results revealed marked regional differences in drug use: Sfax and Nabeul exhibited the highest amphetamine levels, while cannabis (THC) was the most consumed drug across all cities. Methamphetamine use remained low, and cocaine consumption showed localized peaks in Tunis and Ariana. To assess the pandemic's impact, 2021 data were compared with pre-COVID-19 levels from 2019. Post-pandemic trends indicated increased MDMA consumption, particularly during weekends, coinciding with resumed nightlife. A qualitative screening for 32 NPS identified 26 compounds, with synthetic cannabinoids and cathinones most prevalent, and occasional detections of fentanyl analogues, reflecting evolving patterns in recreational drug use. These trends were influenced by socio-economic and demographic differences across regions. This study highlights the value of WBE as an effective rapid surveillance tool for public health surveillance and underscores the lasting effects of COVID-19 on drug consumption behaviors in Tunisia.