Data from: Prevalence of vancomycin-variable Enterococcus faecium (VVE) among vanA-positive sterile site isolates and patient factors associated with VVE bacteremia

Vancomycin-variable enterococci (VVE) are vanA-positive, vancomycin-susceptible enterococci with the ability to revert to a vancomycin-resistant phenotype on exposure to vancomycin. We sought to assess the prevalence of VVE and to determine clinical characteristics of patients infected with VVE. We prospectively collected Enterococcus faecium sterile site isolates from Toronto Invasive Bacterial Diseases Network hospitals from January 2015 to June 2016 and calculated VVE (defined as vanA-positive, vancomycin-susceptible isolates) prevalence among vanA-containing isolates. We performed chart reviews of VVE and vancomycin-resistant E. faecium (VRE) bacteremias identified from January 2012 to June 2016, and on a random sample of patients with bacteremia due to vanA/vanB-negative, vancomycin-susceptible enterococci (VSE) from January 2015 to June 2016. Clinical characteristics were compared and factors associated with mortality assessed. Because of the potential reversion from VVE to VRE, pulsed-field gel electrophoresis (PFGE) was performed for strains causing breakthrough bacteremia in order to identify relatedness among strains with different phenotypic resistance within the same patient. VVE comprised 47% (18/38) of vanA-positive isolates. The charts of 36 VRE, 25 VVE, and 79 VSE patients were reviewed. Central venous catheter associated bacteremia was more common in VVE (44%) and VRE patients (57%) than in VSE patients (28%) (P=0.01). The Pitt bacteremia (OR 1.3, P=0.002) and the Charlson score (OR 1.2, P=0.008) were the only independent mortality predictors. PFGE of strains causing breakthrough bacteremia showed high within-patient clonality, irrespective of vanA-positivity or vancomycin-susceptibility. A substantial proportion of vanA-positive isolates are VVE and are therefore not detected with conventional selective culture methods. Bacteremia sources of patients with VVE are similar to those infected with VRE. We detected no association between VVE and 30-day mortality or breakthrough bacteremia.万古霉素可变肠球菌（Vancomycin-variable enterococci, VVE）是指携带vanA基因、对万古霉素敏感，但在万古霉素暴露后可逆转恢复为万古霉素耐药表型的肠球菌。本研究旨在评估VVE的流行率，并明确VVE感染患者的临床特征。研究于2015年1月至2016年6月期间，从多伦多侵袭性细菌疾病网络（Toronto Invasive Bacterial Diseases Network）所属医院前瞻性收集屎肠球菌（Enterococcus faecium）无菌部位分离株，并计算vanA阳性分离株中VVE（定义为vanA阳性、万古霉素敏感分离株）的占比。我们对2012年1月至2016年6月期间检出的VVE及万古霉素耐药屎肠球菌（vancomycin-resistant E. faecium, VRE）菌血症患者的病历进行回顾，同时对2015年1月至2016年6月期间因vanA/vanB阴性、万古霉素敏感肠球菌（vancomycin-susceptible enterococci, VSE）引起菌血症的患者随机抽样进行病历回顾。对各组患者的临床特征进行比较，并分析与死亡率相关的影响因素。鉴于VVE存在向VRE逆转的潜在可能，针对出现突破性菌血症的菌株，我们开展了脉冲场凝胶电泳（pulsed-field gel electrophoresis, PFGE）检测，以明确同一患者体内表型耐药性不同的菌株之间的亲缘关系。VVE占vanA阳性分离株的47%（18/38）。本研究共回顾了36例VRE、25例VVE及79例VSE患者的病历。中心静脉导管相关性菌血症在VVE患者（44%）和VRE患者（57%）中的发生率显著高于VSE患者（28%）（P=0.01）。皮特菌血症评分（OR=1.3，P=0.002）与查尔森合并症指数（OR=1.2，P=0.008）是仅有的独立死亡率预测因素。针对突破性菌血症菌株的PFGE检测显示，无论菌株是否携带vanA基因或是否对万古霉素敏感，同一患者体内的菌株均呈现高度克隆同源性。相当比例的vanA阳性分离株为VVE，因此常规选择性培养方法无法检出此类菌株。VVE患者的菌血症感染源与VRE感染患者相似。本研究未发现VVE与30天死亡率或突破性菌血症存在相关性。