Invasive Methicillin-Resistant Staphylococcus aureus Infections in the United States

for the Active Bacterial Core surveillance (ABCs) MRSA Investigators A FTER BEING INITIALLY REported among injecting drug users in Detroit in 1981 1 and then associated with the deaths of 4 children in Minnesota and North Da-kota in 1997, 2 community-associated methicillin-resistant Staphylococcus au-reus (MRSA) has become the most frequent cause of skin and soft tissue infections presenting to emergency departments in the United States. 3 Although community outbreaks of MRSA in diverse populations, including Ameri-can Indian and Alaska Natives, 4 sports Context As the epidemiology of infections with methicillin-resistant Staphylococcus aureus (MRSA) changes, accurate information on the scope and magnitude of MRSA infections in the US population is needed. Objectives To describe the incidence and distribution of invasive MRSA disease in 9 US communities and to estimate the burden of invasive MRSA infections in the United States in 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). Main Outcome Measures Incidence rates and estimated number of invasive MRSA infections and in-hospital deaths among patients with MRSA in the United States in 2005; interval estimates of incidence excluding 1 site that appeared to be an outlier with the highest incidence; molecular characterization of infecting strains. Results There were 8987 observed cases of invasive MRSA reported during the surveillance period. Most MRSA infections were health care–associated: 5250 (58.4%) were community-onset infections, 2389 (26.6%) were hospital-onset infections; 1234 (13.7%) were community-associated infections, and 114 (1.3%) could not be classified. In 2005, the standardized incidence rate of invasive MRSA was 31.8 per 100 000 (interval estimate, 24.4-35.2). Incidence rates were highest among persons 65 years There were 1598 in-hospital deaths among patients with MRSA infection during the surveillance period. In 2005, the standardized mortality rate was 6.3 per 100 000 (interval estimate, 3.3-7.5). 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. Conclusions Invasive MRSA infection affects certain populations disproportionately. It is a major public health problem primarily related to health care but no longer confined to intensive care units, acute care hospitals, or any health care institution.