Could the load of carbapenemase genes in hospital wastewater be a proxy for the epidemiology of emerging resistance to carbapenems in humans?

Background Antimicrobial resistance (AMR) poses a growing threat to global public health and is a key concern for infection control teams in hospitals. However, AMR surveillance is time-consuming and limited in most countries, resulting in incomplete findings. In several high-income countries, infection control teams ensure the contact tracing of every patient carrying an emerging extremely resistant bacterium which is very time-consuming. Wastewater surveillance (WWS) has been proposed as an alternative approach for the surveillance of infectious diseases. This study aims to investigate the dynamics of endemic ( bla CTX-M ) and emerging AMR genes ( bla OXA-48 , bla NDM , bla KPC and vanA ) in wastewater under real-world hospital conditions, and to compare results from two hospital buildings with contrasting resistance epidemiology, haematology building versus traumatology / orthopaedic building. Methods The sampling programmes were adapted according to the sampling sites and patient flow for each hospital building. Genes were quantified in the effluent using qPCR and dPCR. Cultivable carbapenemase-producing Gram-negative bacteria were characterised using MALDI-TOF MS and PCR. Results The feasibility of AMR monitoring in wastewater in real hospital conditions was demonstrated by dPCR and qPCR, which produced correlated results. The presence of peaks and the low load of the vanA and bla NDM genes in wastewater (compared to bla CTX-M ) were consistent with their known emerging status, as indicated by national and local epidemiological data. However, the constant presence of bla OXA-48 and bla KPC at levels often higher than those of bla CTX-M in wastewater did not reflect the known epidemiology of these emerging resistances, particularly in the case of bla KPC . Bacterial culture also revealed discrepancies with known epidemiology, with a majority of Citrobacter spp. carrying bla KPC and bla OXA-48 in wastewater, whereas Escherichia coli and bla OXA-48 dominated in patients. Quantifying carbapenemase genes in wastewater was able to differentiate between buildings housing patients with a high or standard risk of emerging AMR. Conclusion Alongside the encouraging findings regarding patient populations and the potential predictive power of AMR WWS, this study identified obstacles that need to be overcome before it can be used for routine surveillance in an infection control hospital context.