MRSA infection appears more widespread than previously thought

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) appears to be more prevalent than previously believed, affecting certain populations disproportionately and is being found more often outside of health care settings, according to a study in the October 17 issue of JAMA, the Journal of the American Medical Association.

MRSA has become the most frequent cause of skin and soft tissue infections among patients presenting to emergency departments in the United States, and can also cause severe, sometimes fatal invasive disease, according to background information in the article. “As the epidemiology of MRSA disease changes, including both community- and health care–associated disease, accurate information on the scope and magnitude of the burden of MRSA disease in the U.S. population is needed to set priorities for prevention and control,” the authors write.

R. Monina Klevens, D.D.S., M.P.H., of the Centers for Disease Control and Prevention, Atlanta, and colleagues conducted a study to determine the incidence of invasive MRSA disease in certain U.S. communities in 2005 and to use these results to estimate the prevalence of invasive MRSA infections in the U.S. The study consisted of a population-based surveillance for invasive MRSA in nine sites participating in the Active Bacterial Core surveillance (ABCs)/Emerging Infections Program Network from July 2004 through December 2005. Reports of MRSA were investigated and classified as either health care–associated (either hospital-onset or community-onset) or community-associated (patients without established health care risk factors for MRSA).

There were 8,987 observed cases of invasive MRSA reported during the surveillance period. Most were health care–associated, with 5,250 (58.4 percent) community-onset infections, 2,389 (26.6 percent) hospital-onset infections, 1,234 (13.7 percent) community-associated infections, and 114 (1.3 percent) that could not be classified. After adjusting for age, race and sex, the incidence rate of invasive MRSA for 2005 was 31.8 per 100,000 persons. Incidence rates overall were highest among persons 65 years and older (127.7 per 100,000), blacks (66.5 per 100,000), and males (37.5 per 100,000). Rates were lowest among persons age 5 to 17 years (1.4 per 100,000).

“Based on 8,987 observed cases of MRSA and 1,598 in-hospital deaths among patients with MRSA, we estimate that 94,360 invasive MRSA infections occurred in the United States in 2005; these infections were associated with death in 18,650 cases,” the authors write.

Molecular testing identified strains historically associated with community-associated disease outbreaks recovered from cultures in both hospital-onset and community-onset health care–associated infections in all surveillance areas.

“In conclusion, invasive MRSA disease is a major public health problem and is primarily related to health care but no longer confined to acute care. Although in 2005 the majority of invasive disease was related to health care, this may change,” the researchers write.

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