Multiplex Polymerase chain reaction to diagnose bloodstream infections in patients after cardiothoracic surgery

Abstract Background: Sepsis and other infectious complications are major causes of mortality and mor-bidity in patients after cardiac surgery. Whereas conventional blood culture (BC) suffers from low sensitivity as well as a reporting delay of approximately 48–72 h, real-time multiplex poly-merase chain reaction (PCR) based technologies like “SeptiFast” (SF) might offer a fast and reliable alternative for detection of bloodstream infections (BSI). The aim of this study was to compare the performance of SF with BC testing in patients suspected of having BSI after cardi-ac surgery. Methods: 279 blood samples from 168 individuals with suspected BSI were analyzed by SF and BC. After excluding results attributable to contaminants, a comparison between the two groups were carried out. Receiver operating characteristic (ROC) curves were generated to de-termine the accuracy of clinical and laboratory values for the prediction of positive SF results. Results: 14.7% (n = 41) of blood samples were positive using SF and 17.2% (n=49) using BC (n.s. [p>0.05]). In six samples SF detected more than one pathogen. Among the 47 microorgan-isms identified by SF, only 11 (23.4%) could be confirmed by BC. SF identified a higher num-ber of Gram-negative bacteria than BC did (28 vs. 12, χ2=7.97, p=0.005). The combination of BC and SF increased the number of detected microorganisms, including fungi, compared to BC alone (86 vs. 49, χ2=13.51, p<0.001). C-reactive protein (CRP) (21.7±11.41 vs. 16.0±16.9 mg/dl, p=0.009), procalcitonin (28.7±70.9 vs. 11.5±30.4 ng/dl, p=0.015), and interleukin 6 (IL 6) (932.3±1306.7 vs. 313.3±686.6 pg/ml, p=0.010) plasma concentrations were higher in patients with a positive SF result. Using ROC analysis, IL-6 (AUC 0.836) and CRP (AUC 0.804) showed the best predictive values for positive SF results. Conclusion: The SF test represent a valuable method for rapid etiologic diagnosis of BSI in patients after cardiothoracic surgery. In particular this method applies for individuals with sus-pected Gram-negative blood stream. Due to the low performance in detecting Gram-positive pathogens and the inability to determine antibiotic susceptibility, it should be used in addition to BC only.