Whole genome sequencing reveals a prolonged and spatially spread nosocomial outbreak of Panton–Valentine leucocidin-positive meticillin-resistant Staphylococcus aureus (USA300)

Summary Background Whole genome sequencing (WGS) helps to better investigate the transmission and characterization of meticillin-resistant Staphylococcus aureus (MRSA) strains. Aim We describe the detection and unfolding of a prolonged and spatially distributed nosocomial outbreak of Panton–Valentine leucocidin (PVL)-positive MRSA ST8 (USA300). Methods The outbreak was detected by the combination of whole genome sequence (WGS)-based typing, which is implemented for routine surveillance of multidrug-resistant bacteria in our institution, and in-depth epidemiological investigation. To investigate the source, processes were observed and environmental sampling performed. To contain the outbreak, regular and direct personal contact with the healthcare workers (HCWs) was maintained and staff education implemented. Findings The outbreak took place between October 2016 and November 2017 and included five patients who were treated in two different departments as inpatients and outpatients; three were infected, two were colonized. Additionally, three HCWs carried the outbreak strain. The strain was not found in the hospital environment. Only through non-mediated communication did the source become apparent. Decolonization of HCWs and infection control measures led to a resolution of the outbreak. Conclusion WGS helped to reveal an outbreak that otherwise might have stayed undetected. Nonetheless, epidemiological investigation is needed to trace the nosocomial transmission. The importance of personal communication in infection control cannot be overstated.