将采血后的血培养瓶立即运送至微生物室,上机培养。血培养样本阳性报警后转种培养18~24 h,挑取单个菌落用VITEK 2 Compact自动化鉴定仪进行细菌鉴定和药物敏感性试验。从BACTEC 9240自动化血培养仪连接的EpiCenter数据库中查询并记录各菌株的TTP。从检验科的实验室信息系统(laboratory information system, LIS)中回顾不同SA菌株对苯唑西林的敏感性,据此判断SA为MRSA或MSSA。
四、统计学方法
运用SPSS 13.0软件进行统计学分析。用Kolmogorov-Smirnov检验判断样本是否为正态分布。用独立样本 t检验比较SA和CoNS的TTP及MRSA和MSSA的TTP。用MedCalc12.4.0软件绘制受试者工作特征(receiver operator characteristic, ROC)曲线,分析TTP的诊断价值。包括确定诊断切点,计算曲线下面积(area under the curve, AUC),进而判断TTP预测不同菌株的准确性。准确性的判断标准如下:AUC>0.9表示准确性较高,0.7≤AUC≤0.9表示准确性为中等,0.5[7]。
参考文献
[1] Naber CK. Staphylococcus aureus bacteremia: epidemiology, pathophysiology, and management strategies[J]. Clin Infect Dis, 2009, 48(Suppl 4): S231-S237.
[2] Laupland KB, Ross T, Gregson DB. Staphylococcus aureus bloodstream infections: risk factors, outcomes, and the influence of methicillin resistance in Calgary, Canada, 2000-2006[J]. J Infect Dis, 2008, 198(3): 336-343.
[3] Thylefors JD, Harbarth S, Pittet D. Increasing bacteremia due to coagulase-negative staphylococci: fiction or reality[J]. Infect Control Hosp Epidemiol, 1998, 19(8): 581-589.
[4] Lai CC, Wang CY, Liu WL, et al. Time to positivity in blood cultures of staphylococci: clinical significance in bacteremia[J]. J Infect, 2011, 62(3): 249-251.
[5] Deleo FR, Otto M, Kreiswirth BN, et al. Community-associated meticillin-resistant Staphylococcus aureus[J]. Lancet, 2010, 375(9725): 1557-1568.
[6] Khatib R, Riederer K, Saeed S, et al. Time to positivity in Staphylococcus aureus bacteremia: possible correlation with source and outcome of infection[J]. Clin Infect Dis, 2005, 41(5): 594-598.
[7] 孙振球, 徐勇勇. 医学统计学[M]. 第2版. 北京: 人民卫生出版社, 2005: 666-667.
[8] 王沛, 何永贵, 陈学兵. 阳性报警时间法快速鉴定血培养中的葡萄球菌[J]. 检验医学, 2009, 24(11): 850-851.
[9] 陈旭, 肖淑珍, 董丹凤, 等. 实时荧光定量PCR在快速检测耐甲氧西林金黄色葡萄球菌中的应用评估[J]. 检验医学, 2012, 27(12): 1035-1039.
[10] Bagel S, Hüllen V, Wiedemann B, et al. Impact of gyrA and parC mutations on quinolone resistance, doubling time, and supercoiling degree of Escherichia coli[J]. Antimicrob Agents Chemother, 1999, 43(4): 868-875.
[11] Lai CC, Wang CY, Liu WL, et al. Time to blood culture positivity as a predictor of drug resistance in Acinetobacter baumannii complex bacteremia[J]. J Infect, 2011, 63(1): 96-98.