Outbreak investigation of community associated methicillin-resistant Staphylococcus aureus in a primary and secondary school in Eastern Switzerland

Background: In 2018 the number of newly detected methicillin-resistant Staphylococcus aureus (MRSA) cases in children attending primary (age 6–12 years) and secondary school (age 13–16 years) nearly doubled compared to previous years. Methods This observation initiated an epidemiological outbreak investigation including a cross-sectional study to determine source of the outbreak, colonization frequency and to identify risk factors for transmission using a questionnaire and to end the outbreak. Results During the investigation, 49 individuals were detected with 57 corresponding isolates. Based on the case definition combined with whole genome sequencing, a core cluster was identified that shared common genetic features and a similar antimicrobial susceptibility pattern (efflux-mediated macrolide resistance, tetracycline susceptibility along with presence of Panton-Valentine leukocidin). Conclusions Epidemiologic evaluation identified a distinct school as a common risk factor. However, the source of the clustered infections within that school could not be further specified. No further cases could be detected after decolonization of infected and colonized children.