Multiplex real-time PCR and blood culture for identification of bloodstream pathogens in patients with suspected sepsis

Abstract

Severe sepsis is increasingly a cause of death. Rapid and correct initial antimicrobial treatment reduces mortality. The aetiological agent(s) cannot always be found in blood cultures (BCs). A novel multiplex PCR test (SeptiFast (alpha version)) that allows identification of 20 bacterial and fungal species directly from blood was used, comparatively with BC, in a multicentre trial of patients with suspected bacterial or fungal sepsis. Five hundred and fifty-eight paired samples from 359 patients were evaluated. The rate of positivity was 17% for BC and 26% for SeptiFast. Ninety-six microorganisms were isolated with BC, and 186 microorganisms were identified with SeptiFast; 231 microorganisms were found by combining the two tests. Of the 96 isolates identified with BC, 22 isolates were considered to be contaminants. Of the remaining 74 non-contaminant BC isolates available for comparison with SeptiFast, 50 were identified as a species identical to the species identified with SeptiFast in the paired sample. Of the remaining 24 BC isolates for which the species, identified in the BC, could not be detected in the paired SeptiFast sample, 18 BC isolates were identified as a species included in the SeptiFast master list, and six BC isolates were identified as a species not included in the SeptiFast master list. With SeptiFast, 186 microorganisms were identified, 12 of which were considered to be contaminants. Of the 174 clinically relevant microorganisms identified with SeptiFast, 50 (29%) were detected by BC. More than half of the remaining microorganisms identified with SeptiFast (but not isolated after BC) were also found in routine cultures of other relevant samples taken from the patients. Future clinical studies should assess whether the use of SeptiFast is of significant advantage in the detection of bloodstream pathogens.

Comparison of three different commercial PCR assays for the detection of pathogens in critically ill sepsis patients

“…In their prospective multicenter study, Westh et al [36] observed more positive PCRbased results for Candida albicans in sepsis patients than in the corresponding blood cultures. Bloos et al [17] published similar findings in their group of critically ill postoperative patients with severe sepsis or septic shock.…”

MASTERMIND: Bringing Microbial Diagnostics to the Clinic

“…Beginning with blood culture collection, there is growing interest and success in direct-from-blood pathogen detection assays. Some progress has already been made in this domain, including SeptiFast [4], IRIDICA [5], and T2 Biosystems [6], although only the last is FDA cleared, and only for detection of Candida species. A MASTERMIND protocol for direct-from-blood pathogen detection could theoretically collect enough blood from each enrolled subject to submit for multiple test evaluations (Figure 3), though required volumes may sometimes be limiting and may not enable a large number of diagnostics to be run on a single specimen.…”

Detection of microbial DNAemia: does it matter for sepsis management?

“…This commercial real-time PCR assay detects 25 bacterial and fungal species or genera that account for [90% of bloodstream pathogens [7]. Observational studies comparing its accuracy to blood culture have indicated a sensitivity ranging between 60 and 95% and specificity between 74 and 83% in hemato-oncology, emergency and critical care settings [9][10][11][12]. PCR took a reported median time of 7-18 h from sampling to result.…”

“…In these studies, many febrile episodes were associated with pathogen DNAemia detected by PCR but not by blood culture. Many of these ''false-positive'' PCR results were deemed clinically significant, based on retrospective patient chart review or subsequent isolation of the pathogen from relevant clinical samples [9][10][11][12].…”