Norway study reveals how hospital sewage is spreading antimicrobial resistance

Antimicrobial resistance (AMR) occurs when microorganisms - bacteria, viruses, fungi, parasites - evolve such that they are no longer affected by medicines such as antibiotics, antivirals and antifungals. AMR is a major global health concern; several once-treatable conditions are now becoming untreatable, increasing the risk of severe illness and death.

AMR is responsible for more than 35,000 deaths each year in the EU. In 2017, the EU adopted the One Health Action Plan against AMR - a unified, integrated approach to health that considers the health of people, animals, and ecosystems as a whole. In 2022, the European Commission and Member States identified AMR as one of their three top-priority health threats, and in 2023, the European Council recommended stepping up EU actions to combat AMR under a One Health approach. In 2025, the EU launched the 10-year Partnership on One Health AMR (OHAMR), a Horizon Europe co-funded initiative that aims to tackle this urgent global health threat via research and innovation.

A study explores how untreated sewage could impact AMR, something that has received little focus to date, using the case study of Norway. Norway has comparatively low levels of antibiotic use both in the EU and globally, a low prevalence of AMR in its clinics, and very limited use of one particular class of antibiotics called carbapenems, which are used as a last resort for micro-organisms that have become resistant to several different drugs. In terms of sewage, Norway does not treat its hospital effluent onsite as many other countries do, providing an opportunity to test untreated hospital sewage for the presence of microorganisms, antibiotics and genetic material that could contribute to microorganisms becoming resistant to treatment.

Researchers collected samples over 24 hours from both raw sewage (influent) and treated sewage (effluent) from Norway's second-largest treatment plant, Holen, which receives sewage from two hospitals. Sewage samples were also collected directly from the sewer line of the Haukeland University Hospital. The samples were analysed for the presence of pathogens and antibiotics. The researchers also assessed the range and number of antibiotic resistance genes (ARGs) within the sample, including genes that arise from microbes' own genetic makeup or through gene transfer from other microbes.

A total of 28 bacterial families were detected across the samples. Researchers found antibiotic-resistant strains of E. coli - a bacterium that causes stomach infections - and Klebsiealla spp. - bacteria that cause pneumonia, blood poisoning and meningitis. These strains were found in both the hospital (untreated) and treated effluent.

Using genetic techniques, the researchers identified 1130 unique ARGs that play a role in developing AMR; these included those that confer resistance against carbapenems. Among these were 349 so-called novel ARGs that were previously unknown and have emerged through evolutionary processes. This indicates that even in a country with a relatively low AMR burden, there is a high diversity of ARGs in hospital effluent that contributes to the spread of AMR - including resistance to last-resort carbapenems - in the receiving environment.

The study found 40 of the ARGs in all three types of sample: raw sewage taken directly from the hospital (untreated), raw sewage going into the treatment plant (untreated), and treated sewage. When only considering hospital and treated effluent, the researchers identified an additional 14 ARGs in both, making 54 in total. This suggests that novel ARGs - ARGs not present in raw sewage entering the plant from elsewhere than the hospital - are introduced to the environment via hospital effluent, and remain even after sewage has been treated.

The method adopted in this study provides an exemplar that other countries and regions could use for AMR monitoring. In 2024, the updated EU directive on urban wastewater treatment addressed the role of urban wastewater in the spread of AMR, mandating Member States to monitor wastewater for AMR to improve understanding and inform policy.

Possible mitigation strategies could include on-site treatment of hospital effluent or removal of particular bacteria from hospital effluent to limit the ongoing dissemination of AMR into the environment. More research is needed to ascertain the role of hospital sewage in AMR in other countries and regions, and to provide detailed insight into which AMGs are present in wastewater. This, in turn, could provide valuable insight into which bacteria and medications pose the greatest risk in terms of contribution to the global health threat of AMR. ***

Reference:

Victor, M.P., Radisic, V., Grevskott, D.H. & Marathe, N.P. (2025) Hospital effluent in a low-resistance setting is responsible for dissemination of novel antibiotic resistance genes into the marine environment. Ecotoxicology and Environmental Safety, Volume 301,118390. https://doi.org/10.1016/j.ecoenv.2025.118390

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"Science for Environment Policy ": European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

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The contents and views included in Science for Environment Policy are based on independent, peer-reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.