Staphylococcus aureus, 2017

Invasive Staphylococcus aureus (SA) infections are classified into one of three categories: hospital-onset (HO-SA), healthcare-associated, community-onset (HACO-SA), and community-associated (CA-SA). SA must be isolated from a normally sterile body site more than 3 days after the date of initial hospital admission for a case to be considered HO-SA. HACO-SA 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-SA cases do not have any identifiable HA risk factors present in the year prior to infection.

In 2005, as part of the EIP Active Bacterial Core surveillance (ABCs) population-based surveillance of invasive methicillin-resistant SA (MRSA) was initiated in Ramsey County; surveillance was expanded to include Hennepin County in 2008. The incidence rate was 14.9 per 100,000 in 2017 (Ramsey: 12.9/100,000 and Hennepin: 15.9/100,000) compared to 11.6 per 100,000 population in 2016. In 2017, MRSA was most frequently isolated from blood (77%, 192/249), and 13% (33/249) of the cases died in the hospital. HACO-MRSA cases comprised the majority (67%, 166/249) of invasive MRSA infections in 2017; CA-MRSA cases accounted for 23% (57/249), and 10% (26/249) cases were HO-MRSA. The median age for all cases was 63 years (range, <1 to 97); the median age was 63 (range, <1 to 88), 66 (range, 16 to 95), and 53 (range, 2 to 97) for HO-, HACO-, and CA-MRSA cases, respectively.

In August 2014, as part of ABCs, population-based surveillance of invasive methicillin-sensitive SA (MSSA) was initiated in Hennepin and Ramsey Counties. The incidence rate was 29.6 per 100,000 in 2017 (Ramsey: 29.5/100,000 and Hennepin: 29.6/100,000) compared to 26.5 per 100,000 population in 2016. In 2017, MSSA was most frequently isolated from blood (75%, 366/491), and 7% (35/491) of the cases died in the hospital. HACO-MSSA cases comprised the majority (49%, 243/491) of invasive MSSA infections in 2017; CA-MSSA cases accounted for 41% (200/491), and 10% (48/491) cases were HO- MSSA. The median age for all cases was 60 years (range, <1 to 99); the median age was 53 (range, <1 to 98), 62 (range, 6 to 99), and 58 (range, <1 to 93) for HO-, HACO-, and CA- MSSA cases, respectively.

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 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 2016, PHL has confirmed 18 VISA cases; 2008 (3), 2009 (3), 2010 (2), 2011 (5), 2013 (3), and 2016 (2). Among all Minnesota VISA cases, 10 (53%) were male and the median age was 64 years (range, 27 to 86). Of those cases with known history, (17), 89% reported recent exposure to vancomycin. No cases of VISA were confirmed in 2017.

• For up to date information see: Staphylococcus aureus
• Full issue>> Annual Summary of Communicable Diseases Reported to the Minnesota Department of Health, 2017