Airborne occurrence and genomic relatedness of multidrug-resistant Staphylococcus epidermidis in hospital wards: a prospective genomic epidemiology study

Background Multidrug-resistant Staphylococcus epidermidis (MDRSE) is an increasing cause of healthcare-associated infections despite enhanced contact-based infection control. Unlike methicillin-resistant Staphylococcus aureus , its incidence has not declined, suggesting transmission pathways remain active. We hypothesize that airborne dispersal may contribute to transmission, with humans as an important reservoir and air serving as a transient transmission pathway. We therefore investigated links between airborne MDRSE, human colonization, and clinical infection in a hospital setting. Methods In a prospective multi-year study at seven sites with suspected MDRSE transmission in a Swedish university hospital, airborne bacteria were quantified using settle plates. In a trauma orthopaedic ward with high airborne MDRSE levels, axillary skin and anterior nares samples were collected from patients and healthcare workers. Whole-genome sequencing was performed on isolates recovered from air, colonized patients, environmental surfaces, and clinical infections to assess genomic relatedness. Results Airborne MDRSE was detected on 50% (12/24) of sampling days in ICU patient rooms and 71% (41/58) of sampling days in the trauma orthopaedic ward, including patient rooms and the adjacent corridor, but was not detected in the operating suite corridors (0/12) or the neonatal ICU (0/12). MDRSE was detected in 17% of orthopaedic patients sampled (8/47) but in none of the healthcare workers (0/57). Among the eight colonized patients, airborne MDRSE was concurrently recovered from the rooms of five (63%); in four of these five patients (80%), colonizing and airborne isolates were closely related, differing by 0–9 SNPs. Out of the 245 non-clinical MDRSE isolates from air, patient colonization, and environmental surfaces, 99.6% (244/245) belonged to hospital-associated lineages (ST2 and ST215). Conclusions The repeated recovery of closely related hospital-associated MDRSE lineages from air, colonization and infection sources suggests that airborne dispersal may contribute to the persistence and circulation of MDRSE in wards caring for patients at risk of device-associated infections, a pathway that warrants further investigation.