Neonatal ICUs
As in adults, neonates may also develop serious infections caused by VRE (132–134). The most
common infection is bacteremia. Meningitis due to VRE has been reported in neonates, and
two cases of VRE meningitis developed in patients after ventriculoperitoneal shunt placement
(133). Urinary tract infection and lower respiratory tract infection with VRE has also been
reported (133). However, there is no evidence that VRE cause pneumonia. Similar to adult
patients, only about 1 in 10 colonized patients develop infection.
Epidemiology of VRE in ICUs
Sources of VRE
The main source/reservoir for VRE in hospitalized patients is the gastrointestinal tract (135–138).
The first sites from which VRE are recovered on culture in newly colonized patients 86%
of the time are the rectum or groin (135). Rectal cultures for VRE remain positive 100% of the
time while patients are hospitalized. Gastrointestinal colonization may be very prevalent in
ICU patients even in the absence of an outbreak (137). Patients with gastrointestinal
colonization with VRE have very high concentrations of VRE in stool (median 10^8 CFU/g)
(136). VRE are the predominant aerobic microorganisms in the gastrointestinal tracts of
colonized patients, outnumbering gram-negative bacilli and vancomycin-susceptible enter-
ococci. Given the high concentrations of VRE in stool, it is not surprising that many body sites
in the patient carrying VRE become colonized (135).
Transmission of VRE in the ICU
Transmission of VRE to patients is by indirect contact with the hands of HCWs and fomites.
There is no evidence that VRE are spread by the airborne route. Five studies show that gloved
hands in contact with colonized patients and their environments become culture positive for VRE
(139–143). When patients have diarrhea, the likelihood of HCWs picking up VRE on their gloves
when in contact with these patients is greater than when in contact with patients who do not have
diarrhea (140). It has also been shown that VRE in the environment surrounding a colonized
patient are easily transferred on to the gloved hands of HCWs after contact with environmental
surfaces (141,143). Isolates from patients, environmental surfaces, and gloved hands of HCWs
were the same strains by PFGE (141). Isolates from patients’ intact skin or environmental surfaces
may also be transferred to clean sites on patients by HCWs’ hands or gloves (142).
Two studies have shown that environmental surfaces have a lower density of VRE than
do perirectal swabs (142,144). Both studies showed that broth amplification was often
necessary to recover VRE from environmental surface samples. However, low density of VRE
on environmental surfaces did not prevent transfer. Sixty-nine percent of surfaces from which
VRE were transferred were positive by broth amplification culture only (142).
Another concern about transfer of VRE from environmental surfaces is that the
microorganism can survive on inanimate surfaces from seven days to two months (145,146).
Further evidence that VRE may survive for a prolonged period on an inanimate surface and then
be transferred to a patient is provided by a report on a VRE outbreak in a burn unit (138). After
initial control of the outbreak for five weeks, the outbreak recurred from an electrocardiogram
(EKG) lead that had not been cleaned since use on the last patient. In the five-week period,
during which the outbreak had been cleared, all weekly patient surveillance cultures and 317
environmental cultures were negative for VRE. The VRE cultured from the EKG lead, the prior
patient on which the lead had been used, and the patient who acquired the VRE from the EKG
lead were shown to be the same strain by PFGE. The time from use of the EKG lead on the first
patient to use on the second patient was 38 days. VRE have also been transmitted between
patients by electronic thermometers during an outbreak (147). Restriction endonuclease analysis
of plasmid DNA indicated that all clinical isolates and isolates from handles of the electronic
thermometers were identical.
Risk Factors for Acquisition of VRE in ICUs
Adult ICUs.Although many published studies have examined risk factors for nosocomial
acquisition of VRE, most have not been well designed. When trying to ascertain risk factors for
MRSA/VRE Colonization and Infection in the Critical Care Unit 113