Types of Infections Caused by MRSA
Infections Caused by HA-MRSA
Adult ICUs.Bacteremia and pneumonia are the most common HA-MRSA infections
encountered when all types of ICUs are considered (41–46). Other HA-MRSA infections
reported include urinary tract infections (41,42), empyema (42), and bacteremia associated
with hemofiltration (45). Surgical site infections due to HA-MRSA are reported from ICUs that
care for surgical patients, although most all of these infections were acquired in the operating
room and not in the ICU (42,43).
Neonatal ICUs.HA-MRSA are recovered from many more sites of infection in patients in
neonatal intensive care units (NICUs) compared with patients in adult ICUs. As is the case in
adult ICUs, reports on sites of infection due to HA-MRSA in neonates are from publications of
outbreak investigations (47–51). Table 1 shows the sites of infection due to HA-MRSA reported
from outbreaks in NICUs.
Infections Caused by CA-MRSA
Adult ICUs.The earliest cases of CA-MRSA acquired in the hospital by adults were reported
from Australia (52–54). There were no reports of outbreaks in the ICUs of these hospitals. More
recent studies report on CA-MRSA in hospitals in the United States and other countries, but
there are no reports of outbreaks due to CA-MRSA in adult ICUs (55,56). Given the invasion of
hospital populations by CA-MRSA and the results of the recently published mathematical
modeling studies on the same, it is likely that CA-MRSA are present in many ICUs and will
account for increasing numbers of MRSA infections in ICUs (22).
Neonatal ICUs.Outbreaks due to CA-MRSA have been reported from NICUs. In one outbreak
nine neonates of low gestational age and birthweight had bacteremia due to CA-MRSA with an
SCCmectype IV but no Panton–Valentine leukocidin (pvl) genes (57). In a second outbreak in an
NICU due to CA-MRSA, the outbreak strain was USA300 and contained thepvlgenes.
Infections included skin and soft tissue abscesses, necrotizing pneumonia, and bacteremia (58).
An outbreak has also been reported in a nursery for newborns and associated maternity
units (59). The isolates from this outbreak were shown to have the type IV SCCmecand genes
for Panton–Valentine leukocidin and staphylococcal enterotoxin K.
Epidemiology of HA-MRSA Infections in Critical Care
Epidemiology of HA-MRSA
Adult ICUs.The risk for adult patients who are culture-negative for HA-MRSA on admission
to an ICU, where HA-MRSA is endemic, for acquiring HA-MRSA ranges between 4.5% and
Table 1 Sites of Infection Due to Nosocomial MRSA in
Patients in Neonatal Intensive Care Units
Sites of infection
Bacteremia
Pneumonia
Skin and soft tissue abscess
Peritonitis or necrotizing enterocolitis
Ventriculitis or meningitis
Osteomyelitis or septic arthritis
Urinary tract infection
Eye infection
Wound infection
Endocarditis
Thrombophlebitis
Ear, nose, and throat infection
Omphalitis
Abbreviation: MRSA, methicillin-resistantStaphylococcus
aureus.
Source: From Refs. 47–51.
104 Mayhall