Invasive MRSA Infection Rates on the Decline

SEPTEMBER 24, 2013
Aimee Simone, Assistant Editor
Infections with methicillin-resistant Staphylococcus aureus associated with hospitalization have dropped dramatically in recent years, while infections picked up in the community have barely declined at all.

Rates of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections, especially those contracted in hospitals, dropped significantly between 2005 and 2011, according to a study published online on September 16, 2013, in JAMA Internal Medicine.
Following previous reports showing a decline in infections, the study used data from the Emerging Infections Program-Active Bacterial Core surveillance system (EIP-ABCs) collected during 2005 and 2011 to better understand current rates of serious MRSA infections in both community and health care settings. The EIP-ABCs, a population-based surveillance system used by the Centers for Disease Control and Prevention, has tracked invasive MRSA infections in 9 US metropolitan areas since 2005.
After collecting information on hospitalization and additional health care risk factors, including presence of a central vascular catheter and history of MRSA infection, surgery, hospitalization, or dialysis, the researchers categorized infections as health care–associated community-onset infections, hospital-onset infections, or community-associated infections. Infections were classified as health care–associated community-onset infections in outpatients with a documented health care risk factor who tested positive for MRSA on or before 3 days after their initial hospital admission. Infections that occurred in patients after 3 days of hospitalization were considered hospital-onset infections. Infections that occurred in outpatients or before 3 days in the hospital without documented health care risk factors were categorized as community-associated infections. Patients with a positive blood culture for MRSA were considered to have bloodstream infections. The researchers calculated national estimates from the data and compared infection rates from 2005 to 2011.
Of 80,461 estimated cases of invasive MRSA infections that occurred nationwide in 2011, approximately 60% were health care–associated community-onset infections, 18% were hospital-onset infections, and 20% were community-associated infections. From 2005 to 2011, the overall estimated rate of invasive MRSA decreased by 31.2%. Health care–associated community-onset infections and hospital-onset infections decreased substantially, by 27.7% and 54.2%, respectively, while community-associated infections decreased by just 5%.
The authors note that this is the first time since the CDC began tracking invasive MRSA infections that the rate for infections contracted in the hospital is lower than the rate for infections among those within the community without health care contact. Although the researchers do not know the exact reason for the large decrease in hospital-onset infections, they suggest that increased awareness and implementation of infection prevention measures in health care settings may be partly responsible. The results also indicate that the United States is on track to achieve the Department of Health and Human Services 2013 goals of reducing health care–associated MRSA infections by 50%. However, more research is needed to better understand the progression of MRSA infections and to further reduce the rate of community-associated infections.
“Despite these decreases, invasive MRSA infections with onset in the community or outpatient setting remain problematic and represent the majority of invasive MRSA infections,” the authors write. “Future research is needed to understand the progression of colonization and noninvasive MRSA infection to invasive infection in outpatient settings.”

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