Hospital acquired vancomycin resistant enterococci in surgical intensive care patients – a prospective longitudinal study

Enterococci are an emerging pathogen in hospitalised patients [1]. These pathogens ubiquitously occur in the hospital environment and show a high tenacity on inanimate surfaces [2‐4]. As a result, enterococcal infections emerge with a rising frequency. Additionally, enterococci have the ability of acquiring resistances to multiple antimicrobial agents and the capacity to transfer resistances to other pathogens via mobile genetic elements [5‐7]. For this reason the prevalence of vancomycin resistant enterococci (VRE) has increased intensively [1]. Vancomycin resistance is associated with enhanced mortality, e.g. among patients with enterococcal blood stream infections [8]. Within hospital settings prevention of VRE transmission is therefore a major objective.

Infection control strategies to control VRE vary, depending on local guidelines. Usually bundle strategies are applied to prevent transmission of VRE between two patients [9]. These include contact precautions, intensified disinfection strategies, the usage of personal protective equipment and active surveillance [10, 11]. In this context, screening strategies are controversially discussed [12]. Both, generalised screening and a risk-adaptive screening, are possible approaches. Regarding the latter, the question arises, which patient groups should be included. Acquisition of VRE in critical ill patients has been associated with prolonged duration of hospital stay, previous hospitalisations, antibiotic treatment, long-term dialysis and immunosuppression [13‐15]. Surgical intensive care patients host a variety of these risk factors, although not explicitly mentioned as risk clientele. Whether surgical intensive care patients per se are at a special risk to acquire VRE and should therefore be included in a risk adapted screening upon subsequent admission to a hospital has not yet been investigated. The present work addresses these questions and investigates risk factors making a VRE acquisition more probable.

Control of VRE is an emerging topic, patients and healthcare workers have to cope with. An important aspect for prevention of transmission is the early recognition of VRE via screening strategies. Here, the question was addressed, whether SICU patients acquire VRE during their stay and which factors put them at special risk for acquisition. VRE acquisition rate (3.0%) on the SICU was lower than the initial prevalence (3.6%) on admission of all patients. Additionally, no hospital-acquired infection but only colonisations occurred. Distribution of detected van-genotypes and MLST ST (vanB-genotype and ST117 were most prevalent) are thereby in accordance with national results and trends published for German healthcare institutions recently [21]. In contrast to another retrospective study investigating hospital-acquired VRE, where the acquisition rate was 28.6%, on different wards including surgical and internal ICUs and lacking a generalised VRE screening, acquisition of VRE in our investigation was comparably low [22]. Further investigations on haemato-oncological patients revealed one third of these patients to develop hospital-acquired VRE [18]. SICU patients should per se not be considered as a specific risk clientele for VRE acquisition in comparison with these patients.

Nevertheless, since hospital-acquired VRE colonisations occurred in our patients, risk factors supporting a VRE acquisition in this group of patients were assessed. Here, the median duration of stay, long-term dialysis and the antibiotic treatment with flucloxacillin or piperacillin/tazobactam were found to be the predominant risk factors. These data correspond with previously investigated risk factors and certainly cannot be considered independently but presuppose each other [23, 24], as also verified by the multivariate analysis. Other risk factors that were found to play an important role in VRE acquisition in other patient clientele could not be verified for our SICU patients. Here, the attributed risk of VRE acquisition after cephalosporin treatment needs to be mentioned. Due to perioperative antibiotic prophylaxis standards, especially referring to cardiac surgery patients, approximately 60% of all admitted patients received cefuroxime; however, this did not lead to an increased VRE acquisition rate. This is noteworthy, since cephalosporine use promotes selection of enterococci and thereby VRE due to intrinsic resistance mechanisms. Nevertheless, previous studies could confirm, that cephalosporine use per se during hospitalization does not result in an enhanced VRE carriage [14]. Interestingly, since the duration of application of flucloxacillin and piperacillin/tazobactam did not vary significantly among the hospital-acquired VRE and the non VRE group, the present results suggest that few antibiotic applications can be sufficient to potentially select VRE. The impact of relatively low numbers of antibiotic administrations on selection of certain pathogens corroborates similar findings for the selection of Clostridium difficile [25].

Previous contacts to VRE confirmed patients are often mentioned as a major risk factor in VRE acquisition [26]. Considering the present core genome analysis of isolates, transmission of VRE on ward could not explicitly be excluded in some cases. This may be due to the transmission of this pathogen on inanimate surfaces in advance to the final diagnosis of the VRE status. Hence in case of a confirmed VRE status, adequate basic and, if necessary, intensified hygienic measures consisting of bundle strategies including contact precautions, usage of personal protective equipment, appropriate disinfection strategies, screening of contact patients and antibiotic stewardship should be implemented to avoid transmissions as good as possible.

Our study has limitations. First, the study period was relatively short. Additional risk factors might have been revealed in case of a longer study period. Moreover, distribution of detected MLST ST in found VRE could have been different. Second, we evaluated risk factors promoting VRE carriage, e.g. flucloxacillin and piperacillin/tazobactam application, but did not investigate the pathophysiological background. Future (prospective) studies are needed to reveal underlying mechanisms. Nevertheless, our findings are in accordance with results published previously [27]. Environmental sampling was not performed during the present study, which could have uncovered the role of inanimate surfaces in VRE transmission, especially in cases of clonality of isolates. Another limitation is the problem of screening sensitivity. Here, only one rectal swab was applied on admission and on discharge respectively, which can lead underestimation of VRE prevalence. However, since screening was performed the same way on admission and on discharge, acquisition rate of VRE during SICU stay can still be assessed precisely.

Compared to patient clienteles previously investigated [23, 28‐30], SICU patients per se are not at higher risk of VRE acquisition if hygiene measures are applied as recommended. If a risk adapted screening policy is applied as practised in other national institutions [22], stay on a SICU should not be considered as a risk factor for screening upon admission to a healthcare facility.