Methicillin-Resistant Staphylococcus aureus (MRSA), 2013

Strains of Staphylococcus aureus that are resistant to methicillin and betalactam antibiotics are referred to as methicillin-resistant S. aureus (MRSA). Traditional risk factors for health care-associated (HA) MRSA include recent hospitalization or surgery, residence in a long-term care facility, and renal dialysis.

In 2005, as part of the EIP Active Bacterial Core surveillance (ABCs), population-based invasive MRSA surveillance was initiated in Ramsey County. In 2005, the incidence of invasive MRSA infection in Ramsey County was 19.8 per 100,000 and was 19.4, 18.5 and 19.9 per 100,000 in 2006, 2007, and 2008, respectively. Surveillance was expanded to include Hennepin County in 2008. The incidence rate for MRSA infection in Ramsey and Hennepin Counties was 17.0, 14.0, 18.2, 14.0, and 12.5 per 100,000 in 2009, 2010, 2011, 2012, and 2013, respectively (2013: Ramsey, 14.6/100,000; and Hennepin, 11.5/100,000). In 2013, MRSA was most frequently isolated from blood (68%); 9% (18/213) of the cases died. The rate of invasive MRSA infection acquired in hospitals (hospital-onset or nosocomial) decreased from 5.4 per 100,000 in 2005 to 1.5 in 2013. Sixteen percent (33/213) of cases reported in 2013 had no reported health care-associated risk factors in the year prior to infection. The overall median age was 60 years (range, <1 to 103); the median age was 52 (range, <1 to 86), 47 (<1 to 92), and 63 (range, 2 to 103) for hospital-onset, community-associated, and health care-associated community-onset, respectively. Please refer to the MDH Antibiogram for details regarding antibiotic susceptibility testing results (pp. 26-27).

Vancomycin-intermediate (VISA) and vancomycin-resistant S. aureus (VRSA) are reportable in Minnesota, as detected and defined according to Clinical and Laboratory Standards Institute approved standards and recommendations: a Minimum Inhibitory Concentration (MIC)=4-8 ug/ml for VISA and MIC ≥16 ug/ml for VRSA. Patients at risk for VISA and VRSA generally have underlying health conditions such as diabetes and end stage renal disease requiring dialysis, previous MRSA infections, recent hospitalizations, and recent exposure to vancomycin. There have been no VRSA cases in Minnesota. We confirmed 1 VISA case in 2000, 3 cases in 2008, 3 cases in 2009, 2 cases in 2010, 5 cases in 2011, and no cases in 2012. In 2013, 3 VISA cases were confirmed; 2 were MRSA and 1 was methicillin-susceptible SA (MSSA). Among all cases, 7 (41%) were male and the median age was 62 years (range, 27 to 62). The 3 2013 cases all reported a history of diabetes, end stage renal disease on hemodialysis, history of MRSA (MSSA for the MSSA case), and recent exposure to vancomycin. The MSSA isolate belonged to a clonal group associated with CA-MRSA (USA300) and the 2 MRSA isolates belonged to a clonal group associated with health-care-associated MRSA types (USA100). All isolates were non-susceptible to daptomycin.

• For up to date information see: Methicillin-resistant Staphylococcus aureus (MRSA)
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2013