Infection Control & Hospital Epidemiology
misses incident colonization.13 We evaluated a practical screening methodology for the detection of asymptomatic VRE coloniza- tion, suitable for use in high-risk patient populations. We sought to compare (1) compliance with perirectal swabbing versus stool sampling, (2) sensitivity of perirectal swabs versus stool samples, and (3) admission-only versus admission-plus-weekly screening.
Methods Study design and setting
We conducted a prospective, patient-level surveillance program of incident VRE colonization in a liver-transplant surgical intensive care unit (SICU) at the Ronald Reagan UCLA Medical Center (RRMC). The RRMC is an urban tertiary-care hospital with 520 beds and 5 adult ICUs. The liver transplant program is a tertiary- care referral center where >150 adult liver transplants are performed annually. The 24-bed liver-transplant SICU had the highest incidence of VRE BSIs among the ICUs.
Monitoring for VRE colonization
In this study, VRE surveillance was conducted from June through August 2015. VRE surveillance began with a point prevalence estimate (all patients present in the SICU when the study began), followed by admission screening and weekly surveillance. Perirectal swabs and stool samples were collected by nursing staff on the day of admission to the SICU (admission screen); the swabs and samples were collected on the same day. Once per week, nursing staff collected an additional perirectal swab and stool sample from all patients in the unit (weekly surveillance). Perirectal swabs were taken around the exterior anal area, without insertion into the rectal vault, with a mini- mum of 1 rotation.
VRE isolation
Perirectal swabs were collected using the Eswab Transport Sys- tem for Aerobic, Anaerobic & Fastidious Bacteria (Becton Dickinson, Sparks MD), and stool samples were collected in C&S medium (modified Cary Blair; Medical Chemical Cor- poration, Torrance, CA). After collection, all samples were refrigerated (4–8°C) until they were sent to the UCLA Clinical Microbiology Laboratory within 24 hours after collection. Upon arrival in the laboratory, Eswab Transport tubes and C&S vials were vortexed completely prior to plating; vortexing of Eswab Transport tubes allows the stool specimen and any organisms in the swab to be released into the transport media present. Using a sterile, plastic transfer pipette, 1 drop (~50 µL) of the vortexed sample was added to 1 quadrant of a Spectra VRE plate (Remel, Lenexa, KS) and was then streaked for isolation. Plates were incubated at 35°C ± 2°C in ambient air for 24 hours and interpreted according to the manufacturer’s instructions: navy blue to pink colonies for E. faecium and light blue colonies indicated E. faecalis. Characteristic colonies were subcultured to tryptic soy agar with 5% sheep blood (BBL, Becton Dickinson) for definitive identification by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF; Vitek MS, bioMérieux, Durham, NC) and susceptibility testing using CLSI reference broth microdilution panels prepared in house. Minimum
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inhibitory concentration (MIC) testing was performed according to CLSI standards.14
VRE strain typing
DiversiLab (DL) typing was performed on paired patient isolates from blood cultures and surveillance cultures. Thereafter, DNA was extracted using an EZ1 DNA Blood Kit (Qiagen, Valencia, CA). Repetitive sequence-based polymerase chain reaction (repPCR) amplification was performed with an Enterococcus DL Fingerprinting Kit according to manufacturer’s instructions (bioMérieux).
Patient data
Demographic and clinical data were collected from medical charts. The Charlson score was used to assess comorbidity, and the Model for End-Stage Liver Disease (MELD) score was used to assess liver disease severity. Statistical analyses were conducted using the McNemar test, the Fisher exact test, the t test, or the χ2 measures of association (Stata software, StataCorp, College Station, TX). A P value<.05 was considered statistically significant. This research was approved by the University of California–Los Angeles Institutional Review Board (UCLA IRB), who determined that informed consent was not required.
Surveillance compliance for admission and weekly surveillance
Compliance measured whether either a perirectal swab or stool sample was collected when required. Compliance was defined as number of samples obtained compared to sample opportunities.
Definition of colonization status
We defined VRE colonization as either a perirectal swab or a stool sample positive for VRE. The sensitivity of the perirectal swabs was defined as the number of VRE colonization events detected by perirectal swabs divided by the number of VRE colonization events detected by either perirectal swab or stool sample. The sensitivity of stool samples was defined likewise. Sensitivity results were compared when a single patient contributed both perirectal swabs and stool samples.
Definition of incident colonization
Incident colonization was defined as a negative screen by peri- rectal swabbing or stool sampling on admission, followed by positive surveillance by either swab or stool. The never-colonized group was defined by a negative screen by swabbing or stool sampling on admission, followed by negative weekly surveillance for all samples collected, including all available swab and stool specimens. The results of the surveillance were not shared with the clinical staff. In the SICU, methicillin-resistant Staphylo- coccus aureus admission screening (but no other pathogen screening) was performed, and VRE admission screening was discontinued in 2013.15 Since 2013, universal chlorhexidine bathing has been conducted daily.16 Patients were treated according to standard infection control policies including contact isolation, dedicated equipment, and the cleaning and disinfecting of the environment.
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