A testing method that uses positive blood cultures and an automated DNA-based polymerase chain reaction and microarray system accurately identified bacteria in sepsis much faster than a standard culture-based process.
The test identified bacterial species in patients with suspected sepsis with 95% sensitivity and 99% specificity, with a mean turnaround time of 23 hours – compared with 41.5-48 hours for the standard culture-based method, according to a report published online Dec. 10 in the Lancet.
Although the sepsis assay is a “major advance” that encompasses the best of nucleic acid and standard culture-based methods, it is unknown yet whether determining the species of a pathogen 18 hours earlier than usual will “translate into demonstrable clinical benefit commensurate to the cost of undertaking the additional test,” commented Dr. Shin Lin of Stanford (California) University and Dr. Samuel Yang of Johns Hopkins University, Baltimore, who were not involved in the study (Lancet 2009 Dec. 10 [doi:10.1016/S0140-6736(09)61791-8]).
In the study, Dr. Päivi Tissari of the Helsinki University Hospital Laboratory and colleagues tested the Prove-it sepsis assay, manufactured by Helsinki-based Mobidiag, against standard blood culture and pathogen identification. The analysis included 3,318 blood samples from patients with suspected sepsis at two large academic medical centers (Lancet 2009 Dec. 10 [doi:10.1016/S0140-6736(09)61569-5]).
The assay identifies more than 50 species of gram-positive and gram-negative bacteria that cause most cases of sepsis.
A total of 2,107 blood culture samples tested positive, including 1,807 that were covered by the sepsis assay. The investigators compared DNA sequences of topoisomerase and 16S rRNA genes and original microbiological laboratory data for samples when the results of the assay and standard blood culture method were not the same.
For organisms that could be detected with the sepsis assay, the results of the assay were between 93% and 100% concordant with the results of blood culturing for all species except one. The assay identified 133 of the 163 coagulase-negative staphylococci that were identified through blood culture.
False-positive results were identified in 52 of the 3,318 samples put through the assay. Those 52 false positives included 34 that were excluded due to contamination or software failure, 11 with more bacterial species detected than with conventional blood culture, 3 with Staphylococcus epidermidis reported instead of coagulase-negative staphylococci, 3 attributed to cross-hybridization between species, and 1 sample in which the assay also detected Bacteroides fragilis.
False-negative results occurred in 34 samples due to inadequate sensitivity for certain species, and in 60 samples because the sepsis assay did not detect all the bacteria it should have. The assay also had difficulty in resolving species in polymicrobial samples.
The median difference in turnaround time between the Prove-it assay and the reference method for 39 samples was 18 hours 19 minutes (range of 17 hours 29 minutes to 43 hours 8 minutes).
The assay provided 100% sensitivity and specificity for methicillin-resistant Staphylococcus aureus, although it is the only type of antibiotic resistance testing that can be performed with the assay, unlike standard biochemical analyses.
“Taking these features into account, the Prove-it sepsis assay cannot replace standard methods but could have a role alongside them,” Dr. Lin and Dr. Yang wrote.
Five of the investigators are employees of Mobidiag, which provided the equipment and reagents for the Prove-it sepsis assay. None of the other researchers had conflicts of interest to declare. Dr. Lin and Dr. Yang had no conflicts of interest to report. The study was performed without outside funding.
Copyright (c) 2009 Elsevier Global Medical News. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
一种使用阳性血培养、自动DNA聚合酶链反应和基因芯片的检测方法可准确鉴定脓毒血症的病原菌，并且较标准培养方法的检测速度大为提高。
根据12月10日在线发表于《柳叶刀》(Lancet)的一篇文章报告，在疑似脓毒血症的患者中使用这种检测方法鉴定细菌种类的灵敏度为95%，特异度为99%，平均检测周期为23h，而标准培养方法的平均检测周期则长达41.5~48h。
尽管这种脓毒血症检测方法是一“重大进步”，其将最先进的核酸分析技术与标准培养方法相结合，但较标准操作提前18h确定病原菌种类能否“转化为与额外检测费用相称的明显临床受益”尚在未知之列，斯坦福大学(加利福尼亚州)的Shin Lin博士和巴尔的摩市约翰霍普金斯大学的Samuel Yang博士评论道，这两位学者均未参与该研究(Lancet 2009 Dec. 10 [doi:10.1016/S0140-6736(09)61791-8])。
在这项研究中，赫尔辛基大学医院实验室的Päivi Tissari博士及其同事将待检验的脓毒血症检测方法与标准血液培养和病原菌鉴定方法进行了比较，待检验方法的设备和试剂均由总部设在赫尔辛基市的Mobidiag公司提供。研究分析了3,318份来自两个大型学术医学中心的疑似脓毒血症患者的血液标本(Lancet 2009 Dec. 10 [doi:10.1016/S0140-6736(09)61569-5])。
在多数脓毒血症患者标本中检出的致病菌为50余种革兰氏阳性和革兰氏阴性细菌。
共2,107份血液培养标本检测结果为阳性，其中包括1,807份采用新的脓毒血症检测方法鉴定为阳性的标本。当这种检测方法与标准血液培养方法所观察到的结果不一致时，研究者将对标本的拓扑异构酶DNA序列、16S rRNA基因和原始微生物学实验室数据进行比较。
关于新的脓毒血症检测方法可检出的微生物，在血液培养方法检出的所有细菌种类中，除1种以外，新方法的检测结果与血液培养方法结果的一致率达到93%~100%。新的检测方法可检出血液培养方法鉴定出的163种凝固酶阴性葡萄球菌中的133种。
在使用新的检测方法分析的3,318份标本中，共52份出现假阳性结果。这52份假阳性标本中包括34份因污染或软件故障而被排除的标本；11份较传统血液培养方法检出更多的细菌种类；3份的结果报告为表皮葡萄球菌，而正确结果应为凝固酶阴性葡萄球菌；3份标本中出现假阳性结果的原因为不同细菌种类之间交叉杂交，在1份标本中，新的检测方法另外检出了脆弱拟杆菌。
在34份标本中，因对某些菌种的灵敏度不足而产生假阴性结果；在另外60份标本中，新的脓毒血症检测方法未能检出所有应检出的菌种。这种方法在处理多种微生物感染标本时也存在缺陷。
对于39份标本，待检验检测方法与参照方法间中位检测周期差异为18h 19min (范围为17h 29min至43h 8min)。
对于甲氧西林耐药的金黄色葡萄球菌，这种检测方法的灵敏度和特异度均为100%，但与标准生物化学分析方法不同，这是此方法可以进行的唯一一种抗生素耐药性检测。
“考虑到这些特征，待检验的脓毒血症检测方法尚无法取代标准方法，但可以与之并行使用，” Lin博士和Yang博士写道。
研究者中的5位受雇于Mobidiag公司，该公司负责提供待检验检测方法所需的设备和试剂。其他研究者均声明无任何利益冲突。Lin博士和Yang博士报告无任何利益冲突。研究未接受任何外来资助。
