Methicillin-Resistant Staphylococcus aureus (MRSA), 2010

Strains of Staphylococcus aureus that are resistant to methicillin and other beta-lactam 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) system, MDH initiated population-based invasive MRSA surveillance 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. In 2008, surveillance was expanded to include Hennepin County. The incidence rate for MRSA infection in Ramsey County was 17.0 per 100,000 in 2009 and 20.0 per 100,000 in 2010; for Hennepin County it was 14.0 per 100,000 in 2009 and 11.3 per 100,000 in 2010. MRSA was most frequently isolated from blood (68%), and 13% (29/232) of cases died. Eleven percent (25/232) of cases had no reported health care-associated risk factors in the year prior to infection. Please refer to the MDH antibiogram for details regarding antibiotic susceptibility testing results (pp. 28-29).

Critical illnesses or deaths due to community-associated (without traditional risk factors) S. aureus infection (both methicillin-susceptible and-resistant) are reportable in Minnesota. Vancomycin-intermediate and vancomycin-resistant S. aureus are also reportable. S. aureus that have developed resistance mechanisms to vancomycin are called vancomycin-intermediate (VISA) or vancomycin-resistant S. aureus (VRSA), as detected and defined according to Clinical and Laboratory Standards Institute (CLSI) approved standards and recommendations (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.

VISA infections are rare, but in the past 2 years there has been an increase in the reported number of cases. MDH confirmed 1 case in 2000, 3 cases in 2008, and 3 cases in 2009. Most of these cases had traditional risk factors for VISA infection including histories of diabetes, non-healing MRSA-positive leg ulcers, end-stage renal disease requiring renal dialysis, and vancomycin use. In 2010, 2 VISA cases were reported. One case was methicillin-susceptible SA (MSSA) and 1 was MRSA. The MRSA case had a history of dialysis, diabetes, and MRSA non-healing ulcers. The MSSA case did not have traditional VISA risk factors including no reported recent history of vancomycin use although this patient did have prolonged exposure to other antibiotics. Both isolates were 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, 2010