MRSA declined between 2005 and 2011, especially hospital-onset infections

There were fewer invasive methicillin-resistant Staphylococcus aureus (MRSA) infections in the U.S. in 2011 than in 2005, and the reduction was greatest for health care-associated infections, a new study found.

Researchers used data from the CDC's Emerging Infections Program-Active Bacterial Core surveillance program to compare MRSA incidence rates from January through December of 2005 and 2011. About 16.5 million people underwent surveillance in 2005 and about 19.4 million underwent surveillance in 2011, in both years from the same nine metropolitan areas. Cases were defined as hospital-onset if a culture was taken after hospital day 3. Health care-associated community onset (HACO) meant a culture was taken as an outpatient on or before hospital day 3 in a patient with a documented health care risk factor. Community-associated cases were the same as HACO cases except patients lacked a documented health care risk factor. Results were published online Sept. 16 by JAMA Internal Medicine.

From 2005 to 2011, hospital-onset infections decreased by 54.2%, HACO infections decreased by 27.7%, and community-associated infections decreased by 5.0%. The combined decrease of invasive MRSA infections was 31.2%, with an estimated 80,461 (95% CI, 69,515 to 93,914) infections in 2011 compared to 111,261 in 2005. In 2011, there were an estimated 48,353 HACO infections, 14,156 hospital-onset infections and 16,560 community-associated infections. Of the community-onset (nondialysis) infections in previously hospitalized patients, 64% occurred within three months after discharge, and 32% of these were admitted from long-term care facilities.

This is the first time since the CDC started tracking MRSA incidence that hospital-onset infections were fewer than community-associated infections, the authors noted. The reduction of hospital-onset infections could be due in part to greater awareness and implementation of infection-prevention measures, they wrote, adding that MRSA infections with community- or outpatient-onset “remain problematic.”

An invited commenter agreed that the study showcased the need for a better understanding of how MRSA strains spread and start infection within the community. “Risks identified in the health care setting do not necessarily translate to those in the community,” he noted.