USA600 (ST45) Methicillin-Resistant Staphylococcus aureus Bloodstream Infections in Urban Detroit
USA600 (ST45) Methicillin-Resistant Staphylococcus aureus Bloodstream Infections in Urban Detroit
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DOI：
10.1128/jcm.00409-10
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发表时间：
2010-06-01
影响因子：
9.4
通讯作者：
Zervos, Marcus J.
中科院分区：
文献类型：
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作者：
Moore, Carol L.;Osaki-Kiyan, Paola;Zervos, Marcus J.
耐甲氧西林金黄色葡萄球菌(MRSA)已成为侵袭性感染的主要来源，每年导致18,000人死亡(9)。据报道，MRSA血流感染(BSI)患者的死亡率为20%至30%，最近一项跨越15年的研究报告的死亡率约为28%(11、12、17)。最近，我们报道了由USA600毒株类型引起的少量MRSA BSI的60%的死亡率，这表明该毒株可能具有独特的毒力特征(5)。USA600，或ST45，在过去十年中首次被报告为在德国和荷兰传播的流行毒株，以前从未与严重感染有关(19-21)。根据我们的初步发现，我们调查了一系列连续的USA600 MRSA BSI病例，以描述感染的患者、治疗和菌株相关特征。在密西西比州底特律一家拥有900张床位的三级保健医院，对420株连续分离的MRSA血流分离株进行了脉冲场凝胶电泳(PFGE)分析，并在2005年7月至2008年7月期间鉴定出16名USA600 MRSA BSI患者(图1)。在研究期间，65%的金黄色葡萄球菌感染是由MRSA引起的。根据美国疾病控制与预防中心的定义，结合临床和实验室结果以及其他诊断试验，通过图表回顾确定了BSI的来源(7)。流行病学分类是根据是否存在医疗保健危险因素以及确定感染是社区感染还是医院感染进行的(8a)。在出现感染时计算每个患者的急性生理学和慢性健康评估II(APACHE II)评分(10)。30天死亡率被定义为在收集指数培养样本后30天内发生的死亡率。微生物学失败的定义是在患者仍在接受治疗的情况下，收集指标培养样本10天后血培养中MRSA的生长。临床失败的定义是30天的死亡率和/或微生物失败。根据类似的定义，在研究期间，本机构MRSA BSI患者的总体临床失败率为23%(5)。每个USA600分离株都进行了PFGE、葡萄球菌盒式染色体微元素(SCCmec)和琼脂糖凝胶分型，并进行了前述(3，4)潘顿-瓦伦丁杀白素(PVL)检测。体外药敏试验根据临床和实验室标准协会制定的标准进行(4)。万古霉素最低抑菌浓度测定采用ETEST法(Bio Merieux，Durham，NC)和人工微量肉汤稀释法(BMD)。用先前建立的方法(4，14)测定万古霉素最小杀菌浓度(MBCs)，并根据孵育24 h后MBC/MIC至少为1：32来确定万古霉素耐受性。如前所述，使用宏观稀释法(MET；BioMerieux，Durham，NC)对分离株进行了异质性万古霉素中间金黄色葡萄球菌(HVISA)表型检测(22)。用这种方法对hVISA表型阳性的分离株进行了如前所述的群体分析。
Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major source of invasive infections, implicated in 18,000 deaths annually (9). Mortality rates of 20 to 30% for patients with MRSA bloodstream infections (BSIs) have been reported, with a recent study, spanning 15 years, reporting a mortality rate of approximately 28%(11, 12, 17). Recently, we reported 60% mortality for a small number of MRSA BSIs caused by the USA600 strain type, suggesting that this strain may have unique virulence characteristics (5). USA600, or ST45, first reported as an epidemic strain spreading throughout Germany and the Netherlands in the last decade, has not been associated previously with serious infection (19–21). Given our preliminary findings, we investigated a series of consecutive cases of USA600 MRSA BSI to describe patient-, treatment-, and strain-related characteristics of the infections. Pulsed-field gel electrophoresis (PFGE) analysis of 420 consecutive MRSA bloodstream isolates was performed, and 16 patients with USA600 MRSA BSIs were identified between July 2005 and July 2008 at a 900-bed tertiary care hospital in Detroit, MI (Fig. 1). During the study period, 65% of all S. aureus infections were caused by MRSA. The source of the BSI was identified by chart review using a combination of clinical and laboratory findings and other diagnostic tests according to CDC definitions (7). Epidemiologic classification was conducted based on the presence or absence of health care risk factors and determination of whether the infection was community or hospital acquired, as described previously (8a).The Acute Physiology and Chronic Health Evaluation II (APACHE II) score was calculated for each patient upon presentation of infection (10). Thirty-day mortality was defined as mortality occurring within the 30 days following collection of the index culture sample. Microbiologic failure was defined by the growth of MRSA in a blood culture 10 days after collection of the index culture sample, while the patient was still on therapy. Clinical failure was defined by 30-day mortality and/or microbiologic failure. According to similar definitions, the overall clinical failure rate for patients with MRSA BSIs at our institution during the study period was 23%(5). Each USA600 isolate underwent PFGE, staphylococcal cassette chromosome mec element (SCCmec), and agr typing and testing for Panton-Valentine leukocidin (PVL) as described previously (3, 4). In vitro susceptibility testing was performed according to standards set by the Clinical and Laboratory Standards Institute (4). Vancomycin MICs were determined by Etest (bioMerieux, Durham, NC) and manual broth microdilution (BMD)(4). Vancomycin minimal bactericidal concentrations (MBCs) were determined using previously established methods (4, 14), and vancomycin tolerance was defined by an MBC/MIC ratio of at least 1: 32 after 24 h of incubation. Isolates were tested for the heterogeneous vancomycin-intermediate S. aureus (hVISA) phenotype by using the macrodilution Etest (MET; bioMerieux, Durham, NC) as described previously (22). Isolates positive for the hVISA phenotype by this method underwent population analysis as described previously