Dr. Burbridge is a Professor of Radiology at the University of
Saskatchewan College of Medicine, and a Radiologist in the Department of
Medical Imaging at the Royal University Hospital in Saskatoon, SK,
Radiology department personnel regularly encounter patients with
infectious diseases via inpatient and outpatient imaging examinations.
These contacts include patients who have been placed on infectious
disease precautions or those who may be carriers of infectious
organisms. Vancomycin-resistant enterococcus (VRE) is a pathogen that
may impact a wide range of radiology department personnel, from those in
patient reception to those in interventional radiology.
Enterococci are spherical bacteria present in large numbers in
the lower gastrointestinal tract of humans. Two common species,
Enterococcus faecalis (E faecalis) and Enterococcus faecium (E faecium),
account for > 85% of the entercocci present in the intestine. E
faecalis is found in concentrations of 105 to 107 colony-forming units
per gram of feces in normal humans.1 Enterococci are hardy
organisms, able to survive on environmental surfaces for extended
periods. Several studies have found multidrug resistant (MDR) strains of
enterococci on various objects in the patient environment, including
bed rails, night tables, curtains, bathroom sinks, toilet seat rings,
electronic thermometers, and other patient-care equipment.2-6
Enterococci are intrinsically resistant to many antibiotics.
Unlike acquired resistance, intrinsic resistance is based upon
chromosomal genes, which typically are nontransferable. Penicillin,
ampicillin, piperacillin, imipenem, and vancomycin are among the few
antibiotics that show consistent inhibitory, but not bactericidal,
activity against E faecalis.
E faecium are less susceptible to β-lactam antibiotics than E
faecalis because the penicillin-binding proteins of the former have
markedly lower affinities for the antibiotics.7-9 Enterococci
have also shown consistent ability to develop antibiotic resistance to a
variety of medications, including ampicillin, gentamicin, and other
aminoglycosides. Enterococci may acquire antibiotic resistance through
exchange of resistance-encoding genes. The first reports of strains
highly resistant to penicillin appeared in the 1980s.9
Thereafter, enterococci were classified as infectious organisms that
demonstrate multiple drug resistance (MDRO) by the Centers for Disease
Control and Prevention (CDC). The past 2 decades have witnessed the
rapid emergence of MDR enterococci. High-level gentamicin resistance
occurred in 1979 and was quickly followed by numerous reports of
nosocomial infection in the 1980s. Simultaneously, sporadic outbreaks of
nosocomial E faecalis and E faecium infection appeared with penicillin
resistance due to β-lactamase production.
Finally, MDR enterococci that had lost susceptibility to
vancomycin were reported in Europe and the United States in the late
1990s.9 Among several phenotypes for vancomycin-resistant
enterococci, VanA (resistance to vancomycin and teicoplanin) and VanB
(resistance to vancomycin alone) are the most common. In the United
States, VanA and VanB account for approximately 60% and 40% of
vancomycin-resistant enterococci (VRE) isolates, respectively.9
Colonization vs. infection
Colonization suggests that the organism is present in or on the
body, but is not causing illness. Infection suggests that the organism
is present in or on the body and is causing illness.10 VRE predominantly resides in the gastrointestinal tract. Colonization rates for VRE range between 3% and 47%.11-13
Traditionally, it was thought that patients developed VRE infection
from their own intestinal source of bacteria, but it has been
demonstrated that the hands of healthcare workers (HCWs) and surfaces in
the healthcare environment can be vectors for spread of the bacteria.4,14
More importantly for radiology, Wood et al demonstrated the presence of
enterococci on radiology department imaging receptors during a random
sampling of equipment from 4 healthcare sites in their region.15
Contamination of x-ray tables, x-ray cassettes, x-ray tubes, portable
x-ray machines, portable ultrasound machines, ultrasound probes, and the
surfaces of the rooms and other equipment seems highly likely and is
probably more common in areas where patients are at increased risk of
harboring and spreading bacteria, such as the operating room and
intensive care units. These sites are frequently visited by mobile
imaging devices and the personnel trained to use them. The risk of
exposure or contamination is probably lower for outpatient imaging, but
there is no guarantee that the patient being imaged is not infected or
colonized. Additionally, the imaging technologist may be colonized or
may have just returned to the department contaminated with enterococci
after exposure to the pathogen in an active care area outside the
imaging department. Thus, the potential for cross-contamination of
outpatients, inpatients, and support personnel must be considered and
MDROs are transmitted by the same routes as
antimicrobial-susceptible infectious agents. Person-to-person
transmission in healthcare settings, usually via the hands of HCWs, is a
major factor in the growth of MDRO incidence and its prevalence in
acute care facilities. Preventing the emergence and transmission of
these pathogens requires a comprehensive approach that includes
administrative involvement and measures, such as staffing, communication
strategies, assessment processes to ensure adherence to infection
control measures, healthcare personnel education and training, judicious
antibiotic use, comprehensive surveillance for targeted MDROs,
application of infection control precautions during patient care,
environmental measures (eg, cleaning and disinfection ), and
decolonization therapy when appropriate.16 For MDROs, (eg, MRSA, VRE), the CDC recommends standard and contact precautions to prevent the spread of these organisms.16
Standard precautions are based on the principle that all bodily
fluids, secretions, excretions, nonintact skin, and mucous membranes may
contain transmissible infectious agents. Standard precautions include
practices that apply to all patients, regardless of suspected or
confirmed infection status, in any setting where healthcare is
delivered. These include: hand hygiene; the use of gloves, gowns, masks,
eye protection, or face shields, depending on the anticipated exposure;
and safe injection practices. Also, items in the patient environment
likely to have been contaminated with infectious body fluids must be
handled in a manner to prevent transmission of infectious agents (eg,
wear gloves for direct contact, and properly clean and disinfect or
sterilize reusable equipment before use on another patient).16
The application of standard precautions is determined by the
nature of the HCW-patient interaction and the anticipated extent of body
fluid or pathogen exposure. For some interactions (eg, performing
venipuncture), only gloves may be needed; during other interactions (eg,
intubation), the use of gloves and a gown, face shield, or mask and
goggles, is necessary. Education and training on the principles and
rationale for recommended practices are critical elements of standard
precautions because they facilitate appropriate decision-making and
promote adherence when HCWs are faced with new circumstances. Standard
precautions are also intended to protect patients by ensuring that
healthcare personnel do not carry infectious agents on their hands or
via equipment used in patient care.16 Table 1 outlines the clinical application of standard precautions in the healthcare setting.
Contact precautions are intended to prevent transmission of
infectious agents, including epidemiologically important microorganisms
that are spread by direct or indirect contact with the patient or the
patient‘s environment. Contact precautions also apply where the presence
of excessive wound drainage, fecal incontinence, or other discharges
from the body suggest an increased potential for extensive environmental
contamination and risk of transmission. A single-patient room is
preferred for patients who require contact precautions. Personnel caring
for patients on contact precautions wear a gown and gloves for all
interactions that may involve contact with the patient or potentially
contaminated areas in the patient‘s room. Donning PPE upon entering the
room and discarding before leaving is done to contain pathogens,
especially those implicated in transmission through environmental
Patient care equipment and instruments/devices
Medical equipment and instruments/devices must be cleaned and
maintained according to the manufacturers‘ instructions to prevent
patient-to-patient transmission of infectious agents. Cleaning to remove
organic material must always precede high-level disinfection and
sterilization of critical and semi-critical instruments and devices
because residual proteinaceous material reduces the effectiveness of
disinfection and sterilization. Noncritical equipment, such as commodes,
intravenous pumps, and ventilators, must be thoroughly cleaned and
disinfected before use on another patient. All such equipment and
devices should be handled in a manner that will prevent HCW contact with
potentially infectious material. It is important to include computers,
and keyboards used for imaging equipment, used in patient care, in
policies for cleaning and disinfection of noncritical items. The
literature on contamination of computers with pathogens has been
summarized and 2 reports have linked computer contamination to
colonization and infections in patients. Although keyboard covers and
washable keyboards are in use, the infection control benefits of those
items and optimal management have not been determined.17-19
As noted earlier, Wood et al have demonstrated the presence of VRE on medical imaging equipment.15
For example, ultrasound probes are optimal vectors for transmission of
infectious agents between patients. They are used for a wide variety of
applications, including portable imaging in the operating room and
intensive care units, neonatal imaging, and localization for
interventional radiology procedures. The probes may encounter dozens of
patients per day. Fowler et al demonstrated the presence of large
bacterial counts on ultrasound probes and the importance of proper probe
cleaning to minimize transmission risk.20
Interventional radiology patients and personnel are at
significant risk for exposure to MDR pathogens via patients with active
infections. The immunocompromised and those with drainage or infusion
devices that are associated with wounds that breech the skin surface, or
that provide access to body cavities or vessels require special
consideration. Nolan, in describing an outbreak of VRE among a group of
pediatric oncology patients, found that one patient was infected while
undergoing an interventional radiology procedure.21
Heightened awareness of infectious disease policies and procedures is
warranted in this department. However, adherence to proper
infection-control guidelines is a significant issue and has been
demonstrated to be inconsistently executed, as described by Reddy et al.22 A
wide variety of procedure-specific guidelines are available, and it
behooves those involved in the management of patients in this arena to
familiarize themselves and others with proper procedures and protocols.
An example of procedure-specific guidelines for intravascular catheters
is provided by O‘Grady et al.23
Sir Francis Bacon stated, “Knowledge is power.” Radiology
departments are a central focus of patient care, and those who work in
this department have the power to minimize the impact of infectious
agents on themselves and others and, in particular, to be sensitive to
the unique preventive policies and procedures for MDROs, such as VRE.
Vigilance and education are both required to slow and halt the spread of
these resistant pathogens and to protect patients and healthcare
workers from their potentially serious effects.
- Noble CJ. Carriage of group D streptococci in the human bowel. J Clin Pathol. 1978;31:1182-1186.
- Karanfil LV, Murphy M, Josephson A, et al. A cluster of
vancomycin-resistant Enterococcus faecium in an intensive care unit.
Infect Control Hosp Epidemiol. 1992;13:195-200.
- Livornese JLL, Dias S, Samel C, et al. Hospital-acquired
infection with vancomycin-resistant Enterococcus faecium transmitted by
electronic thermometers. Ann Intern Med. 1992;117:112-116.
- Noskin GA, Stosor V, Cooper I, Peterson LR. Recovery of
vancomycin-resistant enterococci on fingertips and environmental
surfaces. Infect Control Hosp Epidemiol. 1995;16:577-581.
- Morris Jr. JG, Shay DK, Hebden JN, et al. Enterococci resistant
to multiple antimicrobial agents, including vancomycin: Establishment
of endemicity in a university medical center. Ann Intern Med.
- Yamaguchi E, Valena F, Smith SM, et al. Colonization pattern of
vancomycin-resistant enterococcus faecium. Am J Infect Control.
- Spera RV Jr, Farber BF. Multiple-drug resistant Enterococcus
faecium. The nosocomial pathogen of the 1990s. JAMA. 1992;268:2563-2564.
- Mederski-Samoraj BD, Murray BE. High-level resistance to
gentamicin in clinical isolates of enterococci. J Infect Dis.
- Huycke MM, Sahm DF, Gilmore MS. Multiple-drug resistant
Enterococci: The nature of the problem and an agenda for the future.
Emerg Infect Dis. 1998;4: 239-249.
- Multidrug-resistant organisms in non-hospital healthcare
settings. Centers for Disease Control and Prevention, March 2010.
http://www.cdc.gov/ncidod/dhqp/ar_multidrugFAQ.html. Accessed October
- Handwerger S, Raucher B, Altarac D, et al. Nosocomial outbreak
due to Enterococcus faecium highly resistant to vancomycin, penicillin,
and gentamicin. Clin Infect Dis. 1993;16:750-755.
- Morris JG Jr, Shay DK, Hebden JN, et al. Enterococci resistant
to multiple antimicrobial agents, including vancomycin. Ann Intern Med.
- Edmond MB, Ober JF, Weinbaum DL, et al. Vancomycin-resistant
Enterococcus faecium bacteremia: Risk factors for infection. Clin Infect
- Rhinehart E, Smith N, Wennersten C, et al. Rapid dissemination
of B-Lactamase-producing, Aminoglycoside-resistant Enterococcus faecalis
among patients and staff on an infant-toddler surgical ward. New Eng J
- Wood B, Britt B. Pathogens on image receptors. Radiol Technol. 2010;81:597-598.
- Siegel JD, Rinehart E, Jackson, M, Chiarello L. Guideline for
isolation precautions: Preventing transmission of infectious agents in
healthcare settings 2007. Centers for Disease Control and Prevention
2007. http://www.cdc.gov/ncidod/dhqp/pdf/guidelines/Isolation2007.pdf. Accessed October 2010.
- Neely AN, Weber JM, Daviau P, et al. Computer equipment used in
patient care within a multihospital system: Recommendations for
cleaning and disinfection. Am J Infect Control. 2005;33:233-237.
- Neely AN, Maley MP, Warden GD. Computer keyboards as reservoirs
for Acinetobacter baumannii in a burn hospital. Clin Infect Dis.
- Bures S, Fishbain JT, Uyehara CF, et al. Computer keyboards and
faucet handles as reservoirs of nosocomial pathogens in the intensive
care unit. Am J Infect Control. 2000;28:465-471.
- Fowler C, McCracken D. US probes: Risk of cross infection and
ways to reduce it – comparison of cleaning methods. Radiology.
- Nolan SM, Gerber JS, Zaoutis T, et al. Outbreak of
Vancomycin-resistant Enterococcus colonization among pediatric oncology
patients. Infect Control Hosp Epidemiol. 2009; 30:338-345.
- Reddy P, Liebovitz D, Chrisman H, et al. Infection control
practices among interventional radiologists: Results of an online
survey. Vasc Interv Radiol. 2009; 20:1070-1074.
- O‘Grady NP, Alexander M, Dellinger P, et al. Guidelines for the
prevention of intravascular catheter-related infections. Am J Infect