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

Background: Sepsis and other infectious complications are major causes of mortality and morbidity in patients after cardiac surgery. Whereas blood culture (BC) as the current diagnostic gold standard suffers from low sensitivity as well as a reporting delay of approximately 48–72 h, polymerase chain reaction (PCR) based technologies might offer a fast and reliable alternative for detection of bloodstream infections (BSI). The aim of this study was to compare the performance of real time multiplex-PCR “SeptiFast” (SF), a real-time multiplex PCR assay, with conventional BC testing in patients after cardiac surgery. Methods: 279 blood samples from 168 individuals with suspected BSI were analyzed by SF and BC. Receiver operating characteristic (ROC) curves were generated to determine the accuracy of clinical and laboratory information for the prediction of positive SF results. Results: Excluding results attributable to contaminants, 14.7% (n = 41) of blood samples were positive using SF and 17.2% (n=49) using conventional BC (p= n.s.). In six samples, SF detected more than one pathogen. Among the 47 microorganisms identified by SF, only 11 (23.4%) could be confirmed by BC. SF identified a significantly higher number of Gram-negative bacteria than BC (28 vs. 12, χ2=7.97, p=0.005). The combination of BC and SF significantly increased the number of detected microorganism, including fungi, when 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 (PCT) (28.7±70.9 vs. 11.5±30.4 ng/dl, p=0.015) as well as interleukin 6 (IL 6) (932.3±1306.7 vs. 313.3±686.6 pg/ml, p=0.010) was significantly higher in patients with a positive SF result. In addition, incidence of severe acute kidney injury (AKI) was higher in SF positive than in SF negative patients (31/42 [76%] vs. 125/237 [53%], p=0.01). Using ROC analysis, IL-6 (AUC 0.836) as well as CRP (AUC 0.804), but not PCT showed the best predictive values for positive SF results. Microbiological diagnostic information gained through SF led to 8 therapy adaptations. Conclusion: The real time PCR-based SF test might represent a valuable addition to the traditional BC method for rapid etiologic diagnosis of BSI in patients after cardiothoracic surgery. This powerful method furthermore applies in particular for individuals with fungal infections, Gram-negative bacteremia, AKI and/or elevated CRP and IL-6-concentration. However, due to the low performance in detecting Gram-positive pathogens and the inability to determine antibiotic susceptibility, it should always be used in combination with BC. [1] Key words: Blood stream infection, blood culture, real time multiplex Polymerase Chain Reaction