A Single Negative Result for van Quantitative PCR on Enrichment Broth Can Replace Five Rectal Swab Cultures in Screening for Vancomycin-Resistant Enterococci

Abstract

The increased incidence of infections by vancomycin-resistant Enterococcus (VRE) causes an accumulation of patients who are either colonized with VRE or flagged as potentially colonized with VRE. Since such patients require precautionary isolation upon admission to a hospital, rapid methods to establish VRE colonization status would improve patient care and optimize hospital operation. We evaluated van quantitative PCR (qPCR) on one enrichment broth as a VRE-screening approach. We obtained 255 sets of five rectal specimens from 243 patients. The specimens were cultured using an amoxicillin-containing enrichment broth. Subsequently, a chromogenic agar was incubated and suspect colonies were inoculated on a blood agar plate and characterized by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF), followed by a vancomycin Etest in cases in which Enterococcus spp. were detected. The culturing results were compared with the outcome of van qPCR on all enrichment broths of the first rectal swab. The van qPCR was positive for 43% of the sample sets (vanA, n ϭ 5; vanB, n ϭ 101; vanA and vanB, n ϭ 3). Based on culture data, 20 (7.8%) of the sets were VRE positive in at least one of five samples. The negative predictive value of van qPCR on the first enrichment broth was 99.3%. With a cutoff quantification cycle (C q ) value of Ͼ35 to discriminate negative and positive samples, 87% of the negative patients can be identified within a day after obtaining the sample, compared to 7 days in the culturing approach. VRE screening using qPCR on one enrichment broth can quickly identify non-VRE-colonized patients and therefore decrease costs and limit unnecessary isolation restrictions. KEYWORDS VRE, culturing, qPCR In Europe, the rate of vancomycin-resistant Enterococcus (VRE) colonization on intensive care unit (ICU) admission is estimated at 2.7%, compared to 12.3% in the United States (1). However, VRE prevalence increased significantly in Europe between 2011 and 2014, from 6.2% to 7.9% (2). Although VRE prevalence in The Netherlands is low at 0.9%, 16 VRE hospital outbreaks have been reported to the Signaling Consultation of Hospital acquired Infections and AntiMicrobial Resistance (SO-ZI/AMR) in 2015 (3). Infection control practices for VRE differ globally, but most hospitals give patients who are VRE colonized a VRE flag (4), and this flag stays with the patient upon hospital dismissal until the criteria for removing the flag are met. In The Netherlands, it is common practice to preemptively flag patients who have been in contact with known VRE-colonized patients in an outbreak situation (5). Large outbreaks can result in thousands of patients

Previous antibiotic therapy as independent risk factor for the presence of vancomycin-resistant enterococci in surgical inpatients. Results from a matched case-control study

“…Therefore, we cannot exclude that upon admissions patients were already colonized with VRE. Even if patients are screened upon admission, a single rectal swab for the detection of VRE is not 100% sensitive and repeated swabs or the use of PCR are required in order to obtain a high degree of certainty that VRE are not already present [ 42 ]. Despite we used control plates in order to ensure proper rectal sampling, a single negative swab was sufficient for patients in the control group.…”