Methicillin-resistant Staphylococcus aureus (MRSA): Inpatient

Описание: 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 hospital-associated (HA-MRSA) but the incidence of community-acquired MRSA (CA-MRSA) infections has been growing since the 1990s. The two types of infections exhibit significant genotypical, epidemiological, and clinical differences.

The maps show a steady increase in MRSA prevalence among inpatients in the early 2000s, followed by a plateauing and decline in resistance rates. Although regional variations are similar, MRSA grows considerably slower and falls faster relative to our outpatient sample. In 2000, only three of nine U.S. census divisions report resistance rates in excess of 50%, but by 2004, all regions have passed that mark. Resistance rates exceeding 60% spread from the South Atlantic region eastward into large parts of the Midwest, peaking at 59.5% in 2006. After that, levels decline, reaching pre-2004 levels, with the exception of East South Central (Kentucky, Tennessee, Mississippi, and Alabama), where MRSA continues to grow and accounts for over 70% of all inpatient S. aureus cultures in 2008 and 2009.

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 slower growth of inpatient resistance in the earlier years of the period are part of a larger trend, with CA-MRSA catching up with and replacing hospital-associated strains.* The general leveling off of MRSA rates in the second half of the decade can be attributed to declining rates of health care--associated MRSA. The reasons for the decline are not fully understood but have been linked to growing awareness and improved infection control.

The national average resistance level for the sample was 55.2%, rising from 47% in 2000 to 56% in 2009.

The sample consists of 943,620 inpatient isolates tested for oxacillin resistance. Data are not available from the following states: AR (2008--2009), CO (2006--2009), GA (2007--2009), IA (2008--2009), IN (2007--2009), KY (2007--2009), MS (2007--2009), NV (2009), RI (2000--2004), SD (2005--2009), UT (2007--2009), CT, NH, MT, and WY.

Inpatient samples should not be interpreted as a straightforward proxy for resistance rates of HA-MRSA strains. An increasing share of MRSA infections tends to be hospital-onset community-acquired. That is, patients colonized or infected with a community-associated MRSA strain are hospitalized, and cultures taken from them are classified as "inpatient."