Health care-associated MRSA declining

Rates of invasive health care-associated methicillin-resistant Staphylococcus aureus infections — including hospital-onset invasive disease and health care-associated community-onset disease —declined between 2005 and 2008, Centers for Disease Control researchers reported.

Using data from nine metropolitan Active Bacterial Core surveillance sites, methicillin-resistant Staphylococcus aureus (MRSA) investigators from the Centers for Disease Control’s (CDC’s) Emerging Infections Program performed an active, population-based study of about 15 million people.

The researchers found 21,503 cases of invasive MRSA infections were reported. Results indicated that 57% were health care-associated community-onset, 25% were hospital-onset and 18% were community-associated (CA-MRSA), according to a press release.

Significant decrease

MRSA
A cutaneous abscess caused by methicillin-resistant Staphylococcus aureus bacteria.

Credit: CDC

The data demonstrated a significant decrease from 26% to 23% during the study period for hospital-onset infections (P=.002), the researchers noted, although incidence of health care-associated community-onset disease remained relatively unchanged. Incidence of CA-MRSA, however, rose from 17% to 19%, they reported.

Health care-associated infections totaled 17,508, according to the researchers, with bloodstream infections comprising 88% of reported cases. Of those with bloodstream infections, a number of patients had concomitant infection syndromes, such as pneumonia or empyema, skin and soft tissue infections, bone and joint infections, urinary tract infections and endocarditis.

Analysis revealed that incidence of hospital-onset invasive MRSA infections fell 9.4% per year from 2005 to 2008, and a decrease of 5.7% per year was also observed among health care-associated community-onset infections. These numbers suggest an overall 28% reduction in all hospital-onset MRSA infections and an approximate 17% reduction in all invasive health care-associated community-onset infections during the study period.

Bloodstream infections

Among patients with bloodstream infections, the decrease in yearly incidence was even more noticeable, according to the researchers, with analysis showing an 11.2% decline in hospital-onset and a 6.6% reduction in health care-associated bloodstream infections. These percentages imply a 34% decrease in all hospital-onset MRSA bloodstream infections and a 20% decline in all health care-associated community-onset bloodstream infections.

The researchers also evaluated a subset of patients undergoing dialysis due to high rates of MRSA bloodstream infections among this group. Rates of infection appeared to decrease by 6.4% per year, equating to a 19% decline in these patients during the study period. The researchers noted, however, that most of the numbers responsible for this decrease occurred in 2008.

The researchers suggested that effective implementation of infection prevention interventions may be responsible for the decreasing rates of MRSA found in their study. A change in MRSA strains, such as the shift in prevalence toward USA300, may also contribute to these falling numbers, they noted.

Reference:
Kallen Aj, Mu Y, Bulens S, et al. Health Care–Associated Invasive MRSA Infections, 2005-2008. JAMA.2010;304(6):641-647

Against the backdrop of a perceived inevitable increase in MRSA and increased public awareness of the pathogen and its harms, the report by Kallen et al in this issue of JAMA may help to refocus S. aureus control efforts. The decreases are occurring for a reason, and only by improving existing surveillance and prevention research programs can clinicians and infection control researchers begin to explain why. Such research will be essential for guiding future approaches to all S. aureus prevention. Although MRSA may be in decline, it is unlikely that S. aureus will follow suit.

Eli N. Perencevich, MD, MS, and Daniel J. Diekema, MD
University of Iowa Carver College of Medicine
From an accompanying JAMA editorial

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