Infection Control for MRSA Outbreak

Background: A methicillin-resistant Staphylococcus aureus (MRSA) outbreak occurred in an advanced emergency medical service center between 2010 and 2011. Aim: Our objective was to evaluate the status of the MRSA outbreak, as monitored by molecular analysis. Methods: Twenty-eight MRSA strains were isolated from the blood of 11 patients, and from other specimens (pharynx, nasal cavity, etc) of 12 patients, the environments, and the skin, middle nutus and urine of each one patient from other wards. Pulsed-field gel electrophoresis (PFGE) was performed to evaluate horizontal transmission. Results: Molecular typing by PFGE showed the 28 MRSA strains had 7 patterns, and the PFGE patterns of the 11 MRSA strains were identical. Unselective use of intranasal mupirocin ointment, MRSA monitoring for new inpatients and the prevention of direct or indirect contact infection were performed. However, the number of inpatients with MRSA did not quickly decreased, and additional molecular typing by PFGE showed 10 of 19 MRSA strains (5 of 6 from blood, 5 of 13 from other specimens) were still identical. Lectures and ward rounds were performed repeatedly, and participation in ward rounds by staffs was suggested. Finally, the number of inpatients with MRSA was significantly decreased more than 6 months after the intervention. Although the MRSA outbreak was thought to have ended, follow-up molecular typing by PFGE showed horizontal transmission persisted. Conclusion: our data suggest that various and combined measures of infection control are essential and monitoring by molecular analysis using PFGE is useful to identify the status of a MRSA outbreak.