- 期刊
以實驗診斷方法評估雙套血液培養均為CoNS陽性之意義
Evaluation of Clinical Impact of Two-Set Blood Cultures Positive for Coagulase-negative Staphylococci by Laboratory Methods
摘要
凝固酶陰性的葡萄球菌（Coagulase-negative staphylococcus, CoNS）是血液培養最常見的細菌之一，可能來自污染或是有意義的感染，在臨床上要作正確診斷相當困難。在檢驗室，雙套以上血液培養長出CoNS是目前最常用來鑑別有意義CoNS血流感染的有用指標之一。即便如此，在雙套CoNS的血液培養陽性中，仍有12%～28%可能是由污染所造成。本研究選擇臨床使用非樹脂血瓶、24小時內送檢雙套血液培養、且同時長出CoNS的個案，以脈衝式電泳分析（pulse-field gel electrophoresis, PFGE）的基因分型判讀是否為同源，進一步分析CoNS菌株以API Staph商品套組（bioMe´rieux）鑑定、藥敏試驗表現型、陽性血瓶數、血液培養自動化機台培養呈陽性時間（time to positive, TTP）等指標，作為臨床檢驗室判讀是否真正為CoNS感染的可行性。自2009年8月至2010年5月間，同時長出雙套CoNS的50位病人，共100株細菌中，以PFGE分型結果，不同型為10株，占20%。以pulsotype判讀的結果為標準，細菌鑑定、藥敏試驗表現型、陽性血瓶數（≧3）、TTP（20小時）的敏感性分別為100%、97.5%、95%、77.5%；特異性為60%、90%、70%、80%；陽性預測值為90.9%、97.5%、92.7%、93.9%；陰性預測值為100%、90%、77.8%、47.1%。檢驗室人員可選擇1-2種適合的方法，以幫助醫師正確診斷CoNS引起的血流感染及減少抗生素的使用。
並列摘要
Coagulase-negative staphylococci (CoNS) are frequently isolated from blood cultures. The results may indicate a contamination or true bacteremia. The clinical interpretation of CoNS isolated from blood cultures of a febrile patient is often difficult. According to the literature, the positive findings from both sets of blood cultures may serve as one of the most useful criteria to distinguish true bacteremia from contamination in both clinical and laboratory settings. Even so, approximately 12%~28% of the positive results actually arose from contamination. In this study, CoNS isolated simultaneously from two non-resin blood cultures within 24h were collected for analysis. The genetic relationship of the isolates was examined by pulsed-field gel electrophoresis (PFGE). Based on the pulsotypes, the speciation by a commercial kit (API Staph, bioMe´rieux), antimicrobial susceptibility testing, number of positive blood culture bottles and time to positive (TTP) were further analyzed. Between August 2009 and May 2010, a total of 100 CoNS isolates from 50 patients with two–set positive blood cultures were analyzed by PFGE. Ten (20%) isolates were found to have different pulsotypes. Compared with the results of PFGE typing, the sensitivity of speciation, antibiogram, number of positive blood culture bottles (≧3) and PPT (20 h) was 100%, 97.5%, 95% and 77.5%; the specificity was 60%, 90%, 70% and 80%; the positive predictive value was 90.9%, 97.5%, 92.7% and 93.9%; and the negative predictive value was 100%, 90%, 77.8% and 47.1%, respectively. Laboratory personnel may select 1-2 suitable methods to assist clinicians for the accurate diagnosis of CoNS bacteremia and to reduce the use of antibiotics.