chapter  9
24 Pages

MRSA Bacteremia /

ByMelissa Brunsvold, Lena M. Napolitano

Bacteremia is the third most common nosocomial infection, with urinary

tract infectionmost common, and pneumonia ranking second (1,2). Themost

common causative pathogens for bacteremia are gram-positive pathogens,

accounting for 65% of cases, including coagulase-negative staphylococci

and Staphylococcus aureus (Table 1). The SCOPE project examined 24,179

cases of nosocomial bacteremia in 49U.S. hospitals between 1995 and 2002,

and documented a 10% increase in bacteremia due to gram-positive cocci,

with a concomitant 10% decrease in the percentage of bacteremia due to

gram-negative bacilli (from 33.2% in 1986 to 23.8% in 2003) (4). S. aureus

was the second most common bacteremia isolate after coagulase-negative

staphylococci, accounting for 20% of cases. Most important, the proportion

of methicillin-resistant S. aureus (MRSA) bacteremia isolates increased

from 22% in 1995 to 57% in 2001 (3). In intensive care unit (ICU) patients,

59.5%of all S. aureus isolates associatedwith nosocomial infections are now

methicillin resistant (5). In a U.S. study by the Surveillance Network, annual

rates of MRSA were shown to have increased steadily during 1998-2005,

with rates of up to 59.2%among S. aureus isolates in clinical specimens from

non-ICU patients. In the same study, MRSA constituted 49.1% of blood-

stream S. aureus isolates from inpatients and 41.4% of such isolates from

outpatients (6). Overall rates of S. aureus bacteremia are on the rise; this is

due to a significant increase in the rates of MRSA bacteremia.