Vancomycin-resistant enterococci screening

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The decision about who and when to screen for VRE is a facility-specific decision. CDC recommendations can assist in the determination of a screening strategy appropriate for health care facilities. Infection control personnel at some healthcare facilities selectively screen newly admitted or high-risk patients (e.g., intensive care, oncology, and surgery patients) determined to be at greater risk for VRE colonization.

Screening for VRE can be accomplished in a number of ways. For inoculating peri-rectal/anal swabs or stool specimens directly, one method uses bile esculin azide agar plates containing 6 µg/ml of vancomycin. Black colonies should be identified as an enterococcus to species level and further confirmed as vancomycin resistant by an MIC method before reporting as VRE.

Vancomycin resistance can be determined for enterococcal colonies available in pure culture by inoculating a suspension of the organism onto a commercially available brain heart infusion agar (BHIA) plate containing 6 µg/ml vancomycin. The National Committee for Clinical Laboratory Standards (NCCLS) recommends performing a vancomycin MIC test and also motility and pigment production tests to distinguish species with acquired resistance (vanA and vanB) from those with vanC intrinsic resistance.

Infected patients carry VRE and show clinical signs or symptoms of disease. Colonized patients carry VRE but do not have clinical signs or symptoms of infection. This distinction is important in VRE screening. Patients are usually colonized in the gastrointestinal tract and occasionally in the urinary tract. VRE colony counts are similar in the stool of colonized or infected patients. If a hospital VRE rate is based solely on VRE isolated from clinical cultures (infected patients), the facility may be adequately reporting its infection rate, but may be underestimating the true burden (and therefore potential transmissibility) of VRE in the facility. Screening for patients colonized by VRE provides information about potential sources of illness. The goal of screening is to identify as many colonized patients as possible so that infection control measures can be implemented to decrease transmission and reduce the number of patients infected with VRE.

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