New Irish study reveals frequent transmission of methicillin-susceptible Staphylococcus aureus (MSSA) among healthcare workers, patients and the environment in a large acute hospital under non-outbreak conditions using whole-genome sequencing

Methicillin-resistant Staphylococcus aureus (MRSA) have been endemic in Irish hospitals for several decades and remain a significant clinical issue. A recent collaborative study by microbiologists at the Dublin Dental University Hospital (DDUH), the Irish National MRSA Reference Laboratory at St. James’s Hospital Dublin, and the Department of Clinical Microbiology, Beaumont Hospital Dublin used whole-genome sequencing to investigate transmission of MRSA among patients, healthcare workers (HCWs) and the environment in a large acute hospital over a two-year period. Numerous potential MRSA transmission events were identified in the absence of infection outbreaks. A recently published follow up study on methicillin-susceptible S. aureus (MSSA) recovered during the same period as the MRSA study has just been published on-line by the researchers. MSSA are more diverse and more common than MRSA, and whereas infections caused by MSSA are easier to treat than infections caused by MRSA, MSSA can be just as virulent as MRSA and can cause serious infections.

Numerous potential transmission events associated with a diverse array of MSSA clones were identified in the absence of infection outbreaks. Transmission events involving HCW-to-patient, HCW-to-HCW, patient-to-patient and environmental contamination by HCW/patient isolates were evident. The role of environmental contamination due to shedding by HCWs and/or patients in potential transmission events was a significant factor. It is well documented that approximately one third of healthy people are colonized nasally with S. aureus, either persistently or intermittently. The new study revealed that the mouth was found to be an important reservoir of MSSA, a factor that needs to be incorporated into current routine screening procedures.

Commenting on the significance of the findings, Professor David Coleman from the DDUH Division of Oral Biosciences said: “this and our earlier research shows that numerous transmissions of MRSA and MSSA involving HCWs, patients and the environment occurred in a large acute hospital under non-outbreak conditions, including transmissions that resulted in patient infections. These transmission events would not have been identified using conventional epidemiological tools and demonstrate the power of whole-genome sequencing as a surveillance tool for monitoring the circulation of significant bacterial pathogens in our hospitals”.

Study Authors: P. Kinnevey, A. Kearney, A. Shore, M. Earls, G. Brennan. T. Poovelikunnel, H. Humphreys & D. Coleman

This study was funded by Health Research Board Grant HRA-POR-2015-1051 and has just been published Open-Access on-line in the international journal Journal of Hospital Infection

https://www.journalofhospitalinfection.com/article/S0195-6701(22)00146-3/pdf