Rapid Diagnostic Test Evaluated for Gram-Positive Bloodstream Infections

Overall mortality in patients with Gram-positive bacteremia ranges from 10% to 40%, with delays in effective antimicrobial therapy leading to a dramatic increase in mortality and patients with Gram-positive bacteremia also often suffer from substantial long-term morbidity as a result of prolonged hospitalization and generalized deconditioning.

Scientists at the University of Houston (TX, USA) and their colleagues examined blood cultures submitted as part of routine clinical care to a 650-bed tertiary care hospital. All blood cultures with Gram stain identification of Gram-positive cocci between October and December 2013 were prospectively screened for eligibility. Blood cultures were obtained using BacT/ALERT (bioMérieux; Durham, NC, USA) aerobic (FA) and anaerobic (SN) blood culture bottles and incubated in the bioMérieux BacT/ALERT 3D automatic monitoring system.

The Verigene Gram-positive blood culture assay (BC-GP, Nanosphere, Inc.; Northbrook, IL, USA) is a microarray-based rapid diagnostic test that identifies molecular target through DNA extraction and subsequent hybridization to complementary oligonucleotides present on the microarray grid. A secondary oligonucleotide affixed to a gold nanoparticle is then hybridized to captured bacterial DNA, and the target is identified through analysis of the relative optical density of the probes on the panel. Total hands-on time was approximately 10 minutes with a 2.5-hour test run time.

A total of 143 consecutive patients with Gram-positive bacteremia were included in the analysis. BC-GP correctly identified 127/128 (99.2%) of organisms from monomicrobial blood cultures and 9/14 (64.3%) from polymicrobial, including all methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Stewardship interventions were possible in 51.0% of patients, most commonly stopping or preventing unnecessary vancomycin or starting a targeted therapy.

The authors concluded that the BC-GP is a potentially useful tool for antimicrobial stewardship programs to improve the care of patients with Gram-positive bacteremia. In Monte Carlo simulations, unnecessary antibiotics could be stopped at least 24 hours earlier in 65.6% of cases, and targeted therapy could be started at least 24 hours earlier for 81.2% of the patients. The study was published in the January 2015 issue of the journal Diagnostic Microbiology and Infectious Disease.

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University of Houston
bioMérieux 
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