Clonal dissemination of linezolid-resistant Staphylococcus epidermidis ST22: a retrospective analysis of 24 cases (2017–2021)

Background: Linezolid-resistant Staphylococcus epidermidis (LRSE) outbreaks are increasingly recognized in hospital settings. Observing a rise in LRSE cases, the authors instituted surveillance to detect clonal spread, and evaluated the relationship between linezolid consumption and emergence of resistant. We illustrated transmission dynamics of LRESE by visualising patient movement and overlap Methods: Clinical isolates of S. epidermidis were obtained from patient samples at the Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark. Species identification was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and linezolid resistance was determined by disc diffusion and gradient diffusion testing. All isolates underwent whole-genome sequencing (WGS) to assess genetic relatedness. Patient admission histories were mapped using EpiLinx, a digital platform for visualizing patient movement and overlap within the hospital. Linezolid consumption data were extracted from electronic health records and quantified in defined daily doses (DDD). Findings: In total, 24 patients with at least one clinical LRSE isolate were identified. WGS analysis confirmed that all isolates belonged to a single clone, exhibiting one to 50 single-nucleotide polymorphism differences over a 46-month period. EpiLinx revealed overlapping hospital admissions, facilitating direct transmission. All patients had invasive devices. The Department of Surgical Gastroenterology exhibited notably high linezolid usage than the hospital average at 144.3 DDD/month, accounting for 20% of total hospital consumption. Conclusion: The outbreak was characterized by clonal dissemination of LRSE, strongly associated with elevated linezolid usage in the Department of Surgical Gastroenterology. These findings underscore the critical impact of departmental antibiotic consumption on the emergence and spread of resistant organisms, and highlight the value of real-time genomic surveillance and digital epidemiological tools in outbreak management.