Community-onset, hospital-onset MRSA on the decline

Rates of community-onset and hospital-onset MRSA bacteremia have decreased in parallel. However, the proportion of community-onset skin and soft tissue infections due to MRSA have only recently declined, according to a study published in the Journal of the American Medicl Association.

In an observational study of all Department of Defense Tricare beneficiaries, researchers used record databases to identify and classify all annual first-positive Staphylococcus aureus blood and wound or abscess cultures as methicillin-resistant S. aureus (MRSA) or methicillin-susceptible S. aureus (MSSA) and as community-onset or hospital-onset infections from January 2005 through December 2010. Outcome measures included unadjusted incidence rates per 100,000 person-years of observation, the proportion of infections due to MRSA and annual trends.

Study results showed 2,643 blood and 80,281 wound or abscess annual first-positive S. aureus cultures during 56 million person-years. Per 100,000 person-years, annual incidence rates varied from 3.6 to 6 for S. aureus bacteremia and 122.7 to 168.9 for S. aureus skin and soft tissue infections (SSTIs). Researchers found that annual incidence rates of community-onset MRSA bacteremia decreased from 1.7 per in 2005 to 1.2 per 100,000 person-years in 2010, and annual incidence rates of hospital-onset MRSA bacteremia decreased from 0.7 in 2005 to 0.4 in 2010 per 100,000 person-years.

Seventy-nine percent of the cases of S. aureus bacteremia and 99% of cases of S. aureus SSTIs were accounted for by community-onset infections. Patients 65 years or older had the highest rates of community-onset MRSA bacteremia, while men had higher rates of community-based bacteremia. MRSA caused 58% of community-onset S. aureus SSTIs and 54% of hospital-onset bacteremia.

“These observations, taken together with results from others showing decreases in the rates of health care-associated infections from MRSA, suggest that broad shifts in the epidemiology of S. aureus infections may be occurring,” the researchers concluded. “Additional studies are needed to assess whether these trends will continue, which prevention methods are more effective and to what degree other factors may be contributing.”

For more information:

Landrum ML. JAMA. 2012;308:50-59.

Disclosure: The researchers report no relevant financial disclosures.

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