Methicillin-Resistant Staphylococcus aureus (MRSA), 2014

Strains of Staphylococcus aureus (SA) that are resistant to methicillin and beta-lactam antibiotics are referred to as methicillin-resistant S. aureus (MRSA). Invasive MRSA infections are classified into one of three categories: hospital-onset (HO-MRSA), health care-associated, community-onset (HACO-MRSA), and community-associated (CA-MRSA). MRSA must be isolated from a normally sterile body site 4 or more days after the date of initial hospital admission for a case to be considered HO-MRSA. HACO-MRSA cases have at least one HA risk factor identified in the year prior to infection; examples of risk factors include residence in a long term care facility, recent hospitalization(s), dialysis, presence of an indwelling central venous catheter, and surgery. CA-MRSA cases do not have any identifiable HA risk factors present in the year prior to infection.

In 2005, as part of EIP, population-based surveillance of invasive MRSA was initiated in Ramsey County; surveillance was expanded to include Hennepin County in 2008. There were 260 invasive MRSA cases in these two counties in 2014. The incidence rate increased to 15.1 per 100,000 in 2014 (Ramsey: 15.4/100,000 and Hennepin: 15.1/100,000) compared to 12.5 per 100,000 population in 2013. In 2014, MRSA was most frequently isolated from blood (73%), and 10% (26/262) of the cases died. HACO-MRSA cases comprised the majority (69%, 180/260) of invasive MRSA infections in 2014; CA-MRSA cases accounted for 22% (57/260), and 9% (23/260) of cases were HA-MRSA. The median age for all cases was 62 years (range, <1 to 93); the median age was 66 (range, 17 to 93), 62 (range, <1 to 91), and 65 (range, 8 to 91) for HO-, HACO-, and CA-MRSA cases, respectively.

Vancomycin-intermediate (VISA) and vancomycin-resistant S. aureus (VRSA) are reportable in Minnesota, as detected and defined according to CLSI approved standards and recommendations: a minimum inhibitory concentration (MIC)=4-8 µg/ml for VISA and MIC≥16 µg/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. Prior to 2008, the PHL had confirmed 1 VISA case. Between 2008 and 2013, the PHL confirmed 16 VISA cases; 2008 (3), 2009 (3), 2010 (2), 2011 (5), and 2013 (3). No VISA cases were confirmed in 2014. Among all cases, 8 (47%) were male and the median age was 62 years (range, 27 to 86). Of those cases with known history (15), 80% reported recent exposure to vancomycin.

• 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, 2014