Clinical Utility of Rectal Swabs as a Predictor of Vancomycin-Resistant Enterococcal Infections Requiring Antibiotic Treatment

Background: Vancomycin-resistant enterococcus (VRE) rectal swabs are used to identify patients colonized with this organism in order to designate appropriate contact precautions. Although there is a lack of evidence to demonstrate the ability of the VRE rectal swab to predict infection, some clinicians may use a positive result as supportive data to empirically cover for VRE infection.  This practice leads to initiation of broad spectrum agents without a clear indication.  The purpose of this study is to assess whether the result of a VRE rectal swab can positively and/or negatively predict the presence of VRE infection.

Methods: A prospective, observational study was conducted from November 2012 to March 2013 at a large academic medical center. Patients were eligible for enrollment if they were at least 18 years of age, were admitted to an intensive care unit and had received a VRE rectal swab upon admission.  Patients were excluded if they did not receive a VRE rectal swab or if they received an anti-infective agent with VRE activity in the 7 days prior to the VRE rectal swab.  Patients were followed for 30 days and only during their first admission to the hospital.  Infection was defined as at least 1 positive culture from blood or bile, or bacteruria (WBC>10^5) plus pyuria (>10 WBC/HPF).

Results: 541 patients were evaluated during this time period. 503 patients met inclusion criteria, of which, 447 had a negative VRE rectal swab and 56 had a positive VRE rectal swab. 25% [14/56] of patients developed VRE infection within the positive rectal swab group and 2% [8/447] of patients developed a VRE infection within the negative rectal swab group (p <0.01). The infections included 4 bacteremias, 17 UTIs, and 1 peritoneal infection. The positive and negative predictive values of the rectal swab were 25% and 98%, respectively.  The sensitivity and specificity of the rectal swab were 64% and 91%, respectively.

Conclusion: A negative VRE rectal swab is a useful predictor of a negative VRE clinical culture. The likelihood of a patient having a VRE infection with a positive VRE rectal swab is low, meanwhile, the probability of a negative VRE clinical isolate when the rectal swab is negative is very high.  A negative VRE rectal swab may be a tool to guide empiric antibiotic coverage and support deescalating antibiotics with VRE activity.