Drug-resistant Staphylococcus epidermidis found circulating in hospital air

Multidrug-resistant Staphylococcus epidermidis, an increasingly common cause of healthcare-associated infections, has been repeatedly recovered from the air of hospital wards, according to a prospective genomic epidemiology study published in Antimicrobial Resistance & Infection Control. The findings suggest that air may act as a transient transmission pathway for this resistant bacterium, which has persisted in hospitals despite enhanced contact-based infection control.

The research, led by Micael Widerström and colleagues, was conducted at a Swedish university hospital across seven sites with suspected transmission of multidrug-resistant S. epidermidis (MDRSE). Unlike methicillin-resistant Staphylococcus aureus, whose incidence has declined under control measures, MDRSE has continued to rise, prompting the researchers to investigate whether airborne dispersal contributes to its persistence, with humans serving as an important reservoir.

Airborne bacteria were quantified using settle plates. MDRSE was detected in the air on 50 percent of sampling days in ICU patient rooms (12 of 24 days) and on 71 percent of sampling days in a trauma orthopaedic ward (41 of 58 days), including both patient rooms and the adjacent corridor. By contrast, the bacterium was not detected in the operating suite corridors (0 of 12 sampling days) or the neonatal ICU (0 of 12 sampling days).

To examine the relationship between airborne bacteria and human colonization, the team collected axillary skin and anterior nares samples from patients and healthcare workers in the trauma orthopaedic ward, where airborne MDRSE levels were highest. MDRSE was detected in 17 percent of orthopaedic patients sampled (8 of 47), but in none of the healthcare workers tested (0 of 57).

Whole-genome sequencing was performed on isolates recovered from air, colonized patients, environmental surfaces, and clinical infections to assess genomic relatedness. Among the eight colonized patients, airborne MDRSE was concurrently recovered from the rooms of five, and in four of these five patients the colonizing and airborne isolates were closely related, differing by only 0 to 9 single-nucleotide polymorphisms.

The genomic analysis also revealed a striking pattern of hospital association. Of 245 non-clinical MDRSE isolates recovered from air, patient colonization, and environmental surfaces, 99.6 percent (244 of 245) belonged to hospital-associated lineages, specifically sequence types ST2 and ST215. This indicates that the bacteria circulating in the ward environment were not random environmental organisms but lineages adapted to persist within the hospital.

The authors emphasize that 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. They note that this pathway warrants further investigation rather than drawing definitive conclusions about transmission routes.

The study’s design has important limitations in scope. It was conducted at a single Swedish university hospital, and the detection of closely related isolates in air and on patients demonstrates genomic relatedness rather than proving the direction of transmission.

Nevertheless, the findings add a potentially significant dimension to understanding why MDRSE incidence has not declined despite enhanced contact-based infection control.

Subject of Research: Airborne occurrence and genomic relatedness of multidrug-resistant Staphylococcus epidermidis in hospital wards

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

Article References: Widerström, M., Stegger, M., Monsen, T., Leshyk, V. O., Sieber, R. N., & Johansson, A. F. (2026). Airborne occurrence and genomic relatedness of multidrug-resistant Staphylococcus epidermidis in hospital wards: a prospective genomic epidemiology study. Antimicrobial Resistance & Infection Control. https://doi.org/10.1186/s13756-026-01841-5

Image Credits: AI Generated

DOI: 10.1186/s13756-026-01841-5

Keywords: Staphylococcus epidermidis, multidrug resistance, airborne transmission, hospital infection control, genomic epidemiology, whole-genome sequencing, healthcare-associated infections, bacterial colonization, ICU, infection prevention, Airborne, occurrence