Changing Epidemiology of S. aureus Infections in the U.S.

The emergence of the USA300 strain as an important cause of community-onset methicillin-resistant Staphylococcus aureus (MRSA) infections in the late 1990s and early 2000s profoundly changed the epidemiology of staphylococcal disease, both in the U.S. and worldwide. Although several recent studies have suggested that the incidence of healthcare-associated and hospital-onset MRSA infections may be decreasing, less is known about rates of community-onset S. aureus infections. Investigators recently took advantage of the U.S. Military Health System's integrated electronic health records to assess the epidemiology of S. aureus infections from 2005 through 2010 for all individuals eligible to receive care through this network, including active duty members and reservists, retirees, and their family members.

The study period included >56 million person-years of observation. A total of 2643 blood and 80,281 wound or abscess annual first-positive S. aureus cultures were included in the analyses, with MRSA representing 42% of blood and 58% of wound or abscess S. aureus isolates. Unadjusted rates of community-onset S. aureus bacteremias — both MRSA and methicillin-susceptible (MSSA) — decreased significantly during the study period, as did rates of hospital-onset MRSA bacteremia and skin and soft-tissue infections (SSTIs). No significant overall change was seen in the incidence of community-onset MRSA or MSSA SSTIs; however, the proportion of community-onset SSTIs caused by MRSA decreased significantly beginning in 2007.