Thomas Glück, MD

The polymerase chain reaction assay produced results more rapidly but had lower sensitivity and accuracy than blood culture.

Rapid, accurate identification of pathogens is essential for successful management of patients with bloodstream infections. Blood cultures are the standard diagnostic tool in such situations, but results may take ≥48 hours. Recently, a real-time polymerase chain reaction (PCR) assay targeting bacterial and fungal ribosomal DNA in blood (SeptiFast) was introduced, enabling detection and identification of the most common pathogens within a few hours.

In a prospective, multicenter study involving 795 critically ill patients with 922 episodes of suspected nosocomial bloodstream infections between July 2010 and January 2013, researchers in the U.K. compared the clinical accuracy of SeptiFast with that of conventional blood cultures. In 85% of these episodes, patients were receiving antimicrobial therapy within 48 hours before sampling.

Blood culture and SeptiFast results were positive in 9% and 16% of the episodes, respectively. The PCR assay confirmed the species of only 50% of the organisms identified by blood culture while yielding positive results for 12% of culture-negative samples. With blood cultures as the standard, the posttest probability of identifying a pathogen that grew in blood cultures was only 26% for the PCR assay, but when the PCR assay was negative, there was still a 6% chance of a positive blood culture. Of the pathogens grown in blood cultures, 13% were undetectable by the PCR assay because of technical issues; however, 40% of those that were potentially detectable were still not picked up by the SeptiFast.

Citation(s):

Warhurst G et al. Diagnostic accuracy of SeptiFast multi-pathogen real-time PCR in the setting of suspected healthcare-associated bloodstream infection. Intensive Care Med 2015 Jan; 41:86.