document: glycopeptide resistance was detected in enterococci more than 25 years ago , ; since then , vancomycin - resistant enterococci ( vre ) have become important nosocomial pathogens associated with high mortality and costs , , , . 
   glycopeptide resistance in enterococci is mediated by van genes , with vana and vanb being the most prevalent . 
   several european countries have reported a rising incidence of vre in recent years , , . in denmark , a dramatic increase since 2012 has been due to multiclonal outbreaks of vana - positive enterococcus faecium 
   , . 
   it has been estimated that for every patient with a vre infection detected in a clinical sample , up to ten patients are intestinal carriers of vre . 
   therefore , current guidelines recommend screening of patients at risk and implementation of isolation precautions for vre carriers , . screening relies on selective culturing and/or detection of the resistance genes vana or vanb by pcr . 
   however , substantial indirect savings can be achieved by rapidly available results , as highlighted by a report from france , which compared the management of two simultaneous vre outbreaks on two different wards . 
   several studies have examined the diagnostic accuracy of various assays to detect vana and vanb with or without a previous enrichment step , , , , , , , , . 
   however , sensitivities ranging from 43.5% to 100% and specificities from 79.2% to 99.6% have been reported . 
   in contrast , the specificity of the detection of the vanb gene is considerably lower , , , which is attributed to the presence of vanb - positive anaerobic bacteria , . in our laboratory 
   , we have used a culture - based method using overnight enrichment and subsequent plating on chromogenic agar to screen for vre . in autumn 2014 , 
   prompted by long - lasting vre outbreaks , we implemented the xpert vana / vanb assay performed directly on rectal swabs . 
   this fully automated system integrating dna extraction and real - time pcr provides results within an hour . 
   we used the vana part of the assay to guide rapid implementation of infection control measures . here , we evaluate the diagnostic accuracy of the xpert vana / vanb assay and the impact on infection control decision making . 
   our laboratory serves the primary and secondary sectors of a population of 800 000 inhabitants in the northern part of the capital region of denmark , including four university hospitals with a total number of 1577 beds and covering all internal medicine subspecialties and three intensive care units . 
   the infection control units at these four hospitals are part of the clinical microbiology department and employ six infection control nurses . 
   diagnosis of vre in a clinical sample results in roommate screening and isolation precautions are implemented until results are available . 
   if any roommate is found positive , an outbreak is declared and all patients in the ward are screened weekly until no new patient is diagnosed with vre . during weekly screenings , 
   isolation precautions are implemented as soon as a positive vre result is available . for roommate screening and weekly screening of wards , 
   the routine culture - based screening is supplemented by vana pcr . before transfer of patients from an outbreak ward , 
   pcr is performed and the implementation of isolation precautions is based on the pcr result . for vre - positive patients readmitted within 6 months after the last positive screening sample , isolation precautions are implemented at admission independently from screening results . in the case of readmission 
   > 6 months after the last positive sample , screening is advised and the implementation of isolation precautions is individualized based on screening results and risk factors . in these cases , 
   for phenotypic screening , eswab transport medium was transferred to an enrichment broth ( brain  heart infusion supplemented with 4  mg / l vancomycin and 60  mg / l aztreonam ) either by shaking the flocked swab several times in the enrichment medium or by pipetting 100 l . 
   after overnight incubation , 100 l of the enrichment medium was plated on selective chromogenic agar plates ( chromagartm vre , chromagar , paris , france ) and read after 1 and 2 days of incubation . for vana pcr - positive , but culture - negative samples , the culture protocol was thoroughly repeated . 
   species identification was performed by matrix - assisted laser desorption / ionization time - of - flight mass spectrometry ( biotyper , bruker , bremen , germany ) and a preliminary positive result was given if there was abundant growth of e.  faecium on the selective chromogenic agar . 
   susceptibility testing for vancomycin and teicoplanin was performed by the eucast disc diffusion method   and determination of the mic used a gradient strip ( etest , biomrieux , solna , sweden ) to confirm the vana or vanb phenotype . 
   pcr - based screening was undertaken by the automated system genexpert using the xpert vana / vanb assay ( cepheid ab , solna , sweden ) . 
   one hundred microlitres of the eswab transport medium was added to the sample reagent and further handled as recommended by the manufacturer . in case of invalid or error results ( pcr inhibition or technical error ) , the assay was repeated once . 
   only vana pcr results were reported to the requesting wards as a preliminary result and used for guidance of infection control measures . 
   pcr was performed on the same day if the sample arrived in the laboratory before 16.00  h , all days of the week . 
   sample arrival date , laboratory results , dates of preliminary and final results and sample indications were prospectively collected . for final analysis 
   the impact of the vana pcr result on infection control measures was estimated by calculation of  isolation days saved ( number of days from negative pcr result to final negative culture result ) and  transmission risk days saved ( number of days from positive pcr result to preliminary or final positive culture result ) . the computer program 
   , version 3.0.2 ( r foundation for statistical computing , vienna , austria ; http://www.r-project.org/ ) was used for statistical analysis . 
   for comparison of categorical data , fisher s exact test was used . for comparison of numerical data , unpaired groups , 
   sensitivity , specificity , and positive and negative predictive values with 95% ci were calculated using the r package dtcompair . 
   3 - 3013 - 1217/1/ ) and the danish data protection agency ( record no . 2012 - 58 - 0004 ; heh-2015 - 066 ) . 
   from 30 december 2014 to 15 august 2015 , 1110 vre screening samples from 804 patients were examined both by the culture - based method and by pcr . 
   the samples were from 24 different departments from four different hospitals . in 1067 ( 96.1% ) samples , 
   pcr was performed and reported the same day , the sample was received in the laboratory . 
   the median turnaround time for culture results was 3 days ( mean 3.2 ; range 39 days ) . in 35 ( 3.2% ) samples , 
   invalid or error results were obtained after the first pcr analysis and for 11 ( 1.0% ) samples , repeated analysis did not give a result either . 
   of the 1099 samples where a pcr result was obtained , 152 ( 13.8% ) were positive for the vana gene and 167 ( 15.2% ) were culture - positive for an enterococcus species ( all e.  faecium ) with the vana phenotype ( vancomycin - resistant with mic 256  mg / l and teicoplanin - resistant with mic 8256  mg 
   the vana pcr results in relation to culture results are given in table  1 . 
   the vanb pcr was positive in 247 ( 22.5% ) samples , but only one was culture - positive for enterococcus sp . ( enterococcus faecalis ) with the vanb phenotype ( vancomycin - resistant with mic 128  mg / l and teicoplanin - susceptible with mic 0.5 
   discrepant results between culture and vana pcr were further investigated . in 12 of the 22 pcr - negative samples , from which a vana phenotype e.  faecium was cultured , pcr was repeated on the eswab transport medium and two were found positive with high circles of threshold ( ct ) of 36.9 and 38.2 . 
   pcr was also performed on the isolates from the 20 remaining samples and they were all vana pcr - positive . 
   of the 145 culture - positive samples that had been vana pcr - positive , most ( n  =  135 ) were culture positive after 1 day of incubation of the chromogenic agar , whereas the remaining ten samples ( 6.9% ) were only positive after 2 days of incubation . in comparison , eight of the 22 culture - positive samples that had been pcr - negative ( 36.4% ) only turned positive on the second day of incubation ( fisher 's exact test , p  <  0.001 ) . on the other hand , 
   ct values of the culture - negative sample were significantly higher ( median 32.9 ; range 24.138.3 ) than ct values of the culture - positive samples ( median 22.9 ; range 12.837.8 ) ( wilcoxon rank sum test ; p  <  0.001 ) . 
   to calculate the test accuracy of the xpert vana / vanb assay , culture results complemented with information from the patient s earlier and later samples were used as a reference standard . for the analysis of vana pcr , four of seven 
   true positives : three samples from the same patient from which phenotypically vancomycin - susceptible ( mic 1  mg / l ) , but vana - positive e.  faecium was isolated by non - selective culturing ( unpublished data , holzknecht bj ) and one sample taken under linezolid therapy from a patient with vre culture - positive samples 15 days earlier and 28 days later . 
   the sensitivity of the vana pcr assay was 87.1% ( 95% ci 82.1%92.2% ) , the specificity was 99.7% ( 95% ci 99.3%100% ) and the positive and negative predictive values were 98.0% ( 95% ci 95.8%100% ) and 97.7% ( 95% ci 96.7%98.6% ) , respectively . 
   the specificity and positive predictive value of the vanb part of the assay were low at 77.6% ( 95% ci 75.1%80.1% ) and 0.4% ( 95% ci 0.00%1.2% ) , respectively . 
   the majority of the samples ( n  =  1033 ; 93.1% ) were taken as weekly screening samples from 12 different outbreaks during the study period . 
   thirty - seven ( 3.3% ) were roommate screening samples , 14 ( 1.3% ) were taken at readmission , 13 ( 1.2% ) at transferral from outbreak wards and 13 ( 1.2% ) for other indications ( fig .  1 ) . 
   a total of 141 isolation days could be saved as a consequence of faster available negative pcr results . 
   the saving of time due to rapidly available positive pcr results corresponded to a total of 292 saved transmission risk days . 
   on the other hand , false - negative or false - positive pcr resulted in six additional transmission risk days and 13 additional isolation days ( fig .  1 ) . 
   this study describes the performance and impact of the xpert vana / vanb assay , when performed directly on rectal swabs , in the setting of vana e. faecium outbreaks . 
   of the 1099 samples with available pcr and culture results , only 29 showed discordant results : seven were vana pcr - positive , but culture - negative and 22 were culture - positive , but vana pcr - negative . 
   vancomycin - resistant isolates cultured from samples that had been pcr - negative , were vana pcr - positive , which confirms that false - negative pcr results , when performed directly on the sample , were not due to alterations of the primer binding sites . 
   ct - values of vana pcr - positive , culture - negative samples were significantly higher than ct - values in culture - positive samples . likewise , the culture - positive , but vana pcr - negative samples were significantly more often positive after 2 days of incubation of the chromogenic plate than pcr - positive samples , which might also indicate a lower bacteria count . in the implementation phase of the xpert vana / vanb assay , investigation of vana pcr - positive , culture - negative samples had actually led to a change in the culture protocol from plating 10 l to 100 l of enrichment broth on the chromogenic plates to increase sensitivity ( data not shown ) . 
   using culture results complemented with information from patients follow - up samples as a reference standard , the diagnostic accuracy of the vana part of the xpert vana / vanb assay was excellent and in accordance with previous studies , , . however , one previous , but far smaller , study found both a lower sensitivity and a lower specificity of the assay . as there was only one sample that was culture - positive for vanb - positive vre , we could not fully analyse the diagnostic accuracy of the vanb part of the assay . however , the large proportion ( 22.3% ) of false - positive vanb pcr results is in accordance with previous studies , , , , . 
   first , investigation of vana pcr - positive , culture - negative samples from the same patient led to the isolation of phenotypically vancomycin - susceptible , but vana pcr - positive e.  faecium . 
   an outbreak with a similar strain has been described and infection control management similar to vre seems prudent , . 
   the strengths of the diagnostic accuracy study are the large sample size and the prospective and thorough comparison of the xpert vana / vanb assay with the selective culture method , including further investigation of discordant samples by follow - up samples to define a robust reference standard . 
   however , it has been shown that several outbreak clones and multilocus sequence types are circulating in our region . a systematic study of genetically diverse strains would though be necessary to finally conclude on the generalizability of our results . using the xpert vana / vanb assay , 
   96.1% of screening results were available within 1 day , whereas the median turnaround time for selective culturing was 3 days . 
   based on the time interval between available pcr and culture results , we calculated saved isolation days and saved transmission risk days as a consequence of earlier suspension or implementation of isolation measures . 
   however , these numbers might be overestimated , as patients might have been isolated for other reasons or dismissed from the hospital before results were available . 
   besides saved transmission risk days , earlier available positive screening results from roommates also led to faster outbreak declaration and implementation of additional infection control measures such as screening of all patients , enhanced cleaning , enforcement of hand hygiene and staff teaching . 
   we have seen a faster control of vre outbreaks after the implementation of pcr - based screening . however , as this is part of a bundle approach we can not determine the isolated value of the pcr assay ( mogensen and midttun , infection prevention and control canada 2016 national education conference , poster 84 ) . 
   detailed health economics calculations are beyond the scope of this study . however , considering the assay s official price in denmark of 661 dkk ( approx . 
   89 ) per sample and estimated additional costs per isolation day of 3350 ddk ( approx . 
   451 ) , we feel that saving 141 isolation days and 292 transmission risk days as a result of 1110 pcr analyses is a considerable impact and worth the costs . 
   this is more important when the psychosocial consequences of a vre outbreak situation and isolation precautions for patients and staff members are also taken into account . 
   the vana pcr of the xpert vana / vanb assay had a high diagnostic accuracy and considerable impact on infection control decision making in our setting . 
   ln received non - financial support from roche diagnostics a / s and from msd , outside the submitted work . 
   bjh contributed to conception and design of the study , acquisition and analysis of data and drafting of the manuscript . 
   dsh and joj contributed to conception and design of the study and critical revision of the manuscript . 
   ak contributed to conception of the study , acquisition of data and critical revision of the manuscript .
summary: vancomycin - resistant enterococci ( vre ) are increasingly important nosocomial pathogens and screening for colonization status is a mainstay in infection control . 
   we implemented pcr - based screening during vana - positive enterococcus faecium outbreaks in four university hospitals in copenhagen , denmark . 
   xpertvana / vanb was performed directly on rectal swabs and the vana pcr result was used to guide infection control measures . 
   concurrently , all samples were selectively cultured including an overnight enrichment step . 
   diagnostic accuracy was calculated as well as turnaround time and the impact of the earlier available pcr results on infection control decision making . in all 
   , 1110 samples were analysed . 
   the vana pcr positivity rate was 13.8% and culture positivity rate was 15.2% . 
   the diagnostic accuracy of the vana part of the assay was high with a sensitivity of 87.1% , a specificity of 99.7% , and positive and negative predictive values of 98.0% and 97.7% , respectively . 
   the vanb pcr had a considerably lower specificity of 77.6% and a positive predictive value of 0.4% . in 1067 ( 96.1% ) samples , 
   pcr results were reported within 1 day , whereas median culture turnaround time was 3 days . 
   the saving of time to available results corresponded to 141 saved isolation days and 292 saved transmission risk days . 
   false - negative or false - positive pcr results led to six additional transmission risk days and 13 additional isolation days , respectively.the vana pcr had high diagnostic accuracy and the prompt availability of results gave a considerable benefit for infection control decision making .