Methicillin-Resistant Staphylococcus aureus
Key Points
Î Methicillin-resistant Staphylococcus aureus (MRSA) hospital-
associated infections (HAIs) have been associated with significant
morbidity and mortality.
Î In the United States, the proportion of hospital-associated S. aureus
infections resistant to methicillin remains high.
Î The most recent data from the National Healthcare Safety Network
(NHSN) reports that, from 2009 to 2010, 54.6% of S. aureus central
line–associated bloodstream infections (CLABSIs), 58.7% of S. aureus
catheter-associated urinary tract infections, 48.4% of S. aureus
ventilator-associated pneumonia (VAP) episodes, and 43.7% of
S. aureus surgical site infections (SSIs) were caused by MRSA.
Î The higher morbidity and mortality rates associated with MRSA
are not necessarily due to increased virulence of resistant strains
but rather to other factors, such as delays in initiation of effective
antimicrobial therapy, less effective antimicrobial therapy for resistant
strains, and higher severity of underlying illness among persons with
infection due to resistant strains.
Colonization
Î A substantial proportion of colonized patients will subsequently
develop a MRSA infection, such as pneumonia, soft tissue, or primary
bloodstream infection (BSI). Among adults, this proportion has ranged
from 18%-33%.
Î Among pediatric patients, 8.5% of children found to be colonized on
admission subsequently developed a MRSA infection. In addition,
among patients who acquired MRSA colonization while being cared for
in the pediatric intensive care unit (ICU), 47% subsequently developed
MRSA infection.
Î Risk factors for MRSA colonization include severe underlying illness
or comorbid conditions, prolonged hospital stay, exposure to broad-
spectrum antimicrobials, presence of invasive devices (such as central
venous catheters), and frequent contact with the healthcare system or
HCPs.
Î Recent studies have found that an increasing proportion of hospital-
onset invasive MRSA infections are caused by community strains.
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