Staphylococcus aureus is a common gram-positive bacteria that can cause skin and soft-tissue infections. Methicillin-resistant S. aureus (MRSA) outbreaks have been a growing public health concern since the 1960s, and in the late 2000s, MRSA mortality rates in the United States exceeded the combined death toll of AIDS, tuberculosis, and hepatitis B. Historically, MRSA was primarily acquired in healthcare settings, but the incidence of community-acquired MRSA infections (CA-MRSA) has been growing since the 1990s.

The maps show a sharp increase in MRSA prevalence among outpatients in the early 2000s, followed by a plateauing of resistance rates. In 2000, only four of nine U.S. census divisions report resistance rates in excess of 30%, but by 2004, seven of nine report resistance levels of at least 40%. By 2005, all regions have crossed the 40% resistance threshold, and in East South Central, MRSA accounts for nearly 70% of all S. aureus infections.

The increase in MRSA levels through the mid-2000s has been observed in other surveillance studies and has been associated with the rapid growth in fluoroquinolone use. The leveling off of resistance rates in the second half of the decade is attributed to declining rates of healthcare-associated MRSA. The reasons for the decline are not fully understood but could be linked to growing awareness and improved infection control.

The national average resistance level for the sample was 43.9%, rising from 29.6% in 2000 to 52% in 2009.

The sample consists of 920,135 S. aureus outpatient isolates* tested for oxacillin resistance. Data are not available from the following states: AL (2009), AR (2008–2009), CO (2006–2009), GA (2007–2009), IN (2007–2010), IA (2008–2009), KY (2007–2009), MS (2008–2009), NV (2009), RI (2000–2004), SD (2005–2009), UT (2007–2009), CT, ID, MT, NH, and WY.

* Outpatient samples should not be interpreted as a straightforward proxy for community-associated infection. Healthcare-associated, community onset infections would also be reflected in this sample.