Performance evaluation of InfectID-BSI: A rapid quantitative PCR assay for detecting sepsis-associated organisms directly from whole blood

Abstract

Background: Bloodstream infections (BSIs) (presence of pathogenic organism in blood) that progress to sepsis (life-threatening organ dysfunction caused by the body's dysregulated response to an infection) is a major healthcare issue globally with close to 50 million cases annually and 11 million sepsis-related deaths, representing about 20% of all global deaths. A rapid diagnostic assay with accurate pathogen identification has the potential to improve antibiotic stewardship and clinical outcomes.

Methods: The InfectID-Bloodstream Infection (InfectID-BSI) test is a real-time quantitative PCR assay, which detects 26 of the most prevalent BSI-causing pathogens (bacteria and yeast) directly from blood (without need for pre-culture). InfectID-BSI identifies pathogens using highly discriminatory single nucleotide polymorphisms located in conserved regions of bacterial and fungal genomes. This report details the findings of a patient study which compared InfectID-BSI with conventional blood culture at two public hospitals in Queensland, Australia, using 375 whole blood samples (from multiple anatomical sites, eg. left arm, right arm, etc.) from 203 patients that have been clinically assessed to have signs and symptoms of suspected BSI, sepsis and septic shock.

Findings: InfectID-BSI was a more sensitive method for microorganism detection compared with blood culture (BacT/ALERT, bioMerieux) for positivity rate (102 vs 54 detections), detection of fastidious organisms (Streptococcus pneumoniae and Aerococcus viridans) (25 vs 0), detection of low bioburden infections (measured as genome copies/0.35 mL of blood), time to result (<3 h including DNA extraction for InfectID-BSI vs 16 h-48 h for blood culture), and volume of blood required for testing (0.5 mL vs 40-60 mL). InfectID-BSI is an excellent 'rule out' test for BSI, with a negative predictive value of 99.7%. InfectID-BSI's ability to detect 'difficult to culture' microorganisms re-defines the four most prevalent BSI-associated pathogens as E. coli (28.4%), S. pneumoniae (17.6%), S. aureus (13.7%), and S. epidermidis (13.7%).

Interpretation: InfectID-BSI has the potential to alter the clinical treatment pathway for patients with BSIs that are at risk of progressing to sepsis.

Keywords: Blood culture; Bloodstream infections; Quantitative PCR; Rapid diagnostics; Sepsis; Septic shock; qPCR.