[Table of Contents]

Canada Communicable Disease Report - Supplement
Volume: 23S8
December 1997

INFECTION CONTROL GUIDELINES

Preventing the Spread of Vancomycin-Resistant Enterococci (VRE) in Canada

Guidelines for Preventing the Spread of VRE (adapted from HICPAC)

A. Judicious Use of Vancomycin

Situations in which the use of vancomycin is appropriate or acceptable

1. For treatment of serious infections due to ß-lactam-resistant gram-positive microorganisms. Clinicians should be aware that vancomycin may be less rapidly bactericidal than ß-lactam agents for ß-lactam- susceptible Staphylococcal species.

2. For treatment of infections due to gram-positive microorganisms in patients with life-threatening allergy to ß-lactam antimicrobials.

3. When antibiotic-associated colitis (AAC) fails to respond to metronidazole therapy or if AAC is severe and potentially life-threatening.

4. Prophylaxis, as recommended by the American Heart Association, for endocarditis preceding/during certain procedures involving patients at high risk for endocarditis.

5. Prophylaxis for major surgical procedures involving implantation of prosthetic materials or devices, e.g., cardiac and vascular procedures and total hip replacement, at institutions with a high rate of infections due to methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-resistant S. epidermidis (MRSE). There are very few institutions in Canada where MRSA is endemic⁽⁷⁰⁾.

Situations in which the use of vancomycin should be discouraged

1. Routine surgical prophylaxis other than in a patient with life-threatening allergy to ß-lactam antibiotics.

2. Empiric antimicrobial therapy for a febrile neutropenic patient when an infection is unconfirmed. However, if there is strong evidence at the outset that the patient has an infection due to gram-positive microorganisms (e.g., inflamed exit site of Hickman catheter) and MRSA is endemic in the hospital, vancomycin may be indicated.

3. Treatment in response to a single blood culture positive for coagulase-negative staphylococci (if other blood cultures drawn in the same time frame are negative, or if contamination of the blood culture is likely). Because contamination of blood cultures with skin flora, e.g., S. epidermidis, may lead to vancomycin being administered to patients inappropriately, phlebotomists and other personnel who obtain blood cultures should be trained properly to minimize microbial contamination of specimens.

4. Continued empiric use for presumed infections in patients whose cultures are negative for ß-lactam-resistant gram-positive microorganisms.

5. Systemic or local (e.g., antibiotic lock) prophylaxis for infection or colonization of indwelling central or peripheral intravascular catheters.

6. Selective decontamination of the digestive tract.

7. Eradication of MRSA colonization.

8. Primary treatment of antibiotic-associated colitis (AAC)⁽⁷¹⁾.

9. Routine prophylaxis for very low-birth-weight infants.

10. Routine prophylaxis for patients on continuous ambulatory peritoneal dialysis or hemodialysis.

11. Treatment (chosen for dosing convenience) of infections due to ß-lactam-sensitive gram-positive microorganisms in patients with renal failure.

12. Use of vancomycin solution for topical application or irrigation or for pre-transplant gut decontamination.

B. Educational Program

Information about VRE and other antibiotic- resistant organisms and their potential impact

Information regarding the emergence of VRE as a significant nosocomial pathogen in Europe and the United States should be provided to all hospital staff. This may be done in the context of education about other antibiotic-resistant organisms. Special emphasis should be placed on providing continuing education programs to the medical, nursing, pharmacy, and administrative staff. Information about the epidemiology of VRE, risk to patients, and VRE's impact on antimicrobial prescribing practices and on hospital and financial resources should be emphasized.

Information about the influence of antimicrobial usage on the emergence of VRE and other antibiotic-resistant organisms

Many health care facilities throughout the United States and Canada are facing the increasing emergence of antibiotic-resistant organisms (AROs). The emergence of VRE is but one example of many AROs that are a problem in our population. There are several reasons for the emergence of these AROs⁽⁷²⁾, but paramount has been the selective pressure of intense antimicrobial use, much of it excessive and inappropriate, over the past decade or two.

C. Enhancing the Detection and Reporting of VRE in the Microbiology Laboratory

The ability of the microbiology laboratory to accurately identify Enterococcus species and detect vancomycin resistance is an integral component in recognizing the emergence of VRE colonization and infection in health care facilities. Cooperation and communication between the laboratory and those responsible for infection control is equally important (see Figure 1 for information on response to a report of VRE).

Identification of Enterococcus species

A system for presumptive identification of enterococci on primary isolation media is required in the microbiology laboratory. For laboratories not familiar with identifying VRE, additional tests for motility and pigment production may be required to distinguish E. gallinarum and E. casseliflavus from E. faecium and E. faecalis. For those laboratories not familiar with these methods or if financial resources do not permit such identification, a mechanism should be in place for the prompt referral of organisms to provide an appropriate level of identification with a rapid turnaround time.

Susceptibility testing

Routine testing
Depending on local surveillance and jurisdictional practices, laboratories should ensure that a mechanism is available to determine vancomycin resistance and high level resistance to penicillin and aminoglycosides of isolates from blood and all other clinically important isolates. If resources do not permit routine testing of isolates then periodic surveys of antimicrobial susceptibility to vancomycin should be done, the frequency determined by the local/provincial epidemiologic patterns of VRE. Reliable methods such as agar dilution or broth microdilution rather than automated or disk diffusion testing must be used^(53,73,74).

Confirmatory testing
If VRE is isolated from clinical specimens, the guidelines presented below should be followed. It is important to emphasize that if VRE is found from one body site it can be assumed to be present in multiple body sites. Often, vancomycin resistance is detected before speciation is complete. It is important that species identification and vancomycin resistance are confirmed. Thus, confirmation of vancomycin resistance by repeat antimicrobial susceptibility testing using any of the recommended methods described previously, especially if VRE isolates are unusual in the facility, may be required. Alternatively, one may streak 1 µL of standard inoculum (0.5 McFarland) from an isolated colony of Enterococcus species onto BHI agar containing 6 µg/mL of vancomycin, incubate the inoculated plate for 24 hours at 35° C, and consider any growth indicative of vancomycin resistance^(53,54). The following values set by the NCCLS⁽⁵³⁾ can be used as a guide to confirm VRE:

Susceptible - MIC <= 4 µg/mL

Intermediate - MIC 8-16 µg/mL

Resistant - MIC >= 32 µg/mL

Immediate infection control (IC) notification

During performance of confirmatory susceptibility tests, IC and appropriate patient care personnel should be notified regarding the presumptive identification of VRE. The infection control practitioner should assess whether isolation is required until species identification and vancomycin resistance are confirmed. This preliminary report should be followed by the (final) result of the confirmatory test.

Routine surveillance procedures for detecting VRE where VRE has not been previously detected

Antimicrobial susceptibility survey of clinical isolates
Laboratories should routinely screen for vancomycin resistance in all clinically significant enterococcal isolates obtained within the facility from any body site. Susceptibility tests performed only on enterococci recovered from sterile body sites would detect only a small number of clinical VRE isolates^(43,75).

Culture survey of stools or rectal swabs
In tertiary medical centres and other hospitals with many critically ill patients at high risk of VRE infection or colonization (e.g., intensive care units, oncology units, transplant patients), periodic culture surveys of stools or rectal swabs of such patients can detect the appearance of VRE. Fecal screening is recommended even when VRE infections have not been identified clinically, because gut colonization may occur in patients in a facility before infections are identified^(76,77). The frequency and intensity of surveillance should be based on the size of the population at risk, the specific hospital unit(s) involved, the prevalence of VRE in the area, and the cost-benefit ratio of screening.

Screening procedures for detecting VRE when a first isolate of VRE has been detected

The finding of a first isolate of VRE should prompt fecal screening (stool survey or rectal swabs) for the identification of other colonized patients in an effort to establish the optimal and timely application of isolation precautions and control measures. It must be emphasized that the use of screening surveys are merely a tool to elucidate the epidemiology of VRE within a given ward, patient population or facility and are not considered a mandatory component of an infection control program. The optimal timing and extent of screening procedures remains unknown. Currently, there are no data available on cost-effectiveness. Consideration of patient populations, risk factors for acquisition of VRE, and the costs and resources available within the facility must be taken into consideration when implementing screening procedures. As a minimum, stools or perirectal swabs may be obtained from roommates and other close contacts of patients found to be newly colonized with VRE. Additional screening of patients on the same ward or unit may also be considered. In outbreak situations, it may be necessary to screen patients outside of the ward to avoid missing colonized patients. The utility of massive screening efforts directed at all possible contacts, entire health care facility patient populations and staff is unknown at this time and such efforts are not currently recommended.

D. Infection Control Precautions to Prevent the Transmission of VRE in the Health Care Setting

The infection control practitioner or other responsible individual must be aware that there are several different Enterococcus species. However, E. faecalis and E. faecium represent the species most often associated with disease and nosocomial transmission. Laboratories unfamiliar with speciation and susceptibility testing of enterococci may not correctly differentiate E. faecalis and E. faecium from other VRE that do not warrant the same infection control precautions. Practitioners must confirm that their laboratory uses methods that will reliably identify these other species of Enterococcus (e.g., gallinarum, casseliflavus) that are intrinsically resistant to low levels of vancomycin. Enterococcus gallinarum (E. gallinarum) and E. casseliflavus are less likely to be pathogens, their resistance has never been observed to transfer to other bacteria, and they do not require isolation, as do other VRE. If the laboratory identifies a VRE, the practitioner must confirm that it has been identified to species level, by a reference laboratory if necessary. VRE isolates should be confirmed as such by laboratories experienced in enterococci identification and genotyping.

The presence of any isolate of VRE other than E. gallinarum and E. casseliflavus (VRE positive) from a single patient should receive prompt attention by infection control or other responsible personnel, and the ensuing guidelines should be initiated (Figure 1).

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