Tracing Antimicrobial Resistance Across the Hospital–Wastewater–River Continuum: A Pre-COVID-19 and Pandemic-Era Study in Bucharest, Romania

Hospital and municipal wastewaters can transport antimicrobial-resistant bacteria from human-associated sources into receiving aquatic environments, yet longitudinal evidence of their occurrence across the COVID-19 transition remains limited in Eastern Europe. We analyzed seven Bucharest-area sampling campaigns from June 2019 to March 2021 across hospital wastewater, the Glina municipal wastewater treatment plant (WWTP), and the Dâmbovița River. Culture-based abundances of extended-spectrum beta-lactamase (ESBL), carbapenem resistance (CARBA), OXA-48, and vancomycin-resistant enterococci (VRE) screening phenotypes were compared between four pre-COVID-19 and three pandemic-era campaigns. During the pandemic era, ESBL and several carbapenem-resistance screening phenotypes were detected in all three Glina effluent campaigns, whereas detection was generally intermittent before COVID-19. Under the baseline non-detect convention, median effluent abundances were 2.12–4.12 log10 units higher during the COVID-19 era for selected ESBL, CARBA, and OXA screening phenotypes. These descriptive differences were estimated from only four pre-COVID-19 and three COVID-19-era campaigns and were sensitive to assumptions regarding non-detects and sampling formats. Under the original non-detect substitution convention, median CARBA non-fermenter treatment-associated reduction decreased from 2.29 to 0.38 log10 units, while VRE showed inconsistent influent–effluent patterns, including a negative median concentration difference (−1.76 log10 units) during the pandemic era. Downstream river samples exceeded upstream levels for several phenotypes across most campaigns, whereas hospital effluent remained a high-AMR compartment without a uniform pandemic-era increase. These findings highlight municipal effluent and the receiving-water interface as important surveillance points and support integrated AMR monitoring across the urban wastewater continuum.