Ziegler Ingrid, Fagerström Anna, Strålin Kristoffer, Mölling Paula
Department of Infectious Diseases, Örebro University Hospital, Örebro, Sweden.
School of Health and Medical Sciences, Örebro University, Örebro, Sweden.
PLoS One. 2016 Dec 20;11(12):e0167883. doi: 10.1371/journal.pone.0167883. eCollection 2016.
The Magicplex Sepsis Real-time Test (MST) is a commercial multiplex PCR that can detect more than 90 different pathogens in blood, with an analysis time of six hours. The aim of the present study was to evaluate this method for the detection of bloodstream infection (BSI). An EDTA whole blood sample for MST was collected together with blood cultures (BC) from patients with suspected sepsis at the Emergency Department of a university hospital. Among 696 study patients, 322 (46%) patients were positive with at least one method; 128 (18%) were BC positive and 268 (38%) were MST positive. Considering BC to be the gold standard, MST had an overall sensitivity of 47%, specificity of 66%, positive predictive value (PPV) of 23%, and a negative predictive value of 87%. Among the MST positive samples with a negative BC, coagulase-negative staphylococci (CoNS) and species that rarely cause community-acquired BSI were frequently noted. However, the quantification cycle (Cq) values of the MST+/BC- results were often high. We thus hypothesized that the performance of the MST test could be improved if the Cq cut-off level was adjusted downwards. With a lower Cq cut-off value, i.e. 6.0 for Staphylococcus species and 9.0 for all other species, the number of MST positive cases decreased to 83 (12%) and the overall sensitivity decreased to 38%. However, the PPV increased to 59% and the specificity increased to 96%, as many MST positive results for CoNS and bacteria that rarely cause community-acquired BSI turned MST negative. In conclusion, our study shows that with a lower Cq cut-off value, the MST will detect less contaminants and findings with unclear relevance, but to the cost of a lower sensitivity. Consequently, we consider that a positive MST results with a Cq value above the adjusted cut-off should be interpreted with caution, as the result might be clinically irrelevant. In a correspondent way, quantitative results could probably be useful in the interpretation of positive results from other molecular assays for the detection of BSI.
Magicplex脓毒症实时检测（MST）是一种商业化的多重PCR技术，可检测血液中90多种不同病原体，分析时间为6小时。本研究的目的是评估该方法在检测血流感染（BSI）方面的性能。在一所大学医院急诊科，从疑似脓毒症患者中采集用于MST检测的乙二胺四乙酸（EDTA）全血样本，并同时进行血培养（BC）。在696例研究患者中，322例（46%）患者至少有一种检测方法呈阳性；128例（18%）血培养阳性，268例（38%）MST检测阳性。以血培养为金标准，MST的总体敏感性为47%，特异性为66%，阳性预测值（PPV）为23%，阴性预测值为87%。在MST检测阳性但血培养阴性的样本中，经常发现凝固酶阴性葡萄球菌（CoNS）和很少引起社区获得性BSI的菌种。然而，MST+/BC-结果的定量循环（Cq）值通常较高。因此，我们推测，如果下调Cq截断水平，MST检测的性能可能会得到改善。将Cq截断值降低，即葡萄球菌属为6.0，其他所有菌种为9.0时，MST检测阳性病例数降至83例（12%），总体敏感性降至38%。然而，由于许多CoNS和很少引起社区获得性BSI的细菌的MST阳性结果转为阴性，PPV升至59%，特异性升至96%。总之，我们的研究表明，降低Cq截断值时，MST检测到的污染物和相关性不明确的结果会减少，但敏感性会降低。因此，我们认为，Cq值高于调整后截断值的MST阳性结果应谨慎解读，因为该结果可能在临床上不具有相关性。相应地，定量结果可能有助于解释其他用于检测BSI的分子检测方法的阳性结果。
