Performance evaluation of the Verigene® (Nanosphere) and FilmArray® (BioFire®) molecular assays for identification of causative organisms in bacterial bloodstream infections

Molecular assays designed to provide bacterial identification and detection of resistance genes directly from positive blood cultures can significantly reduce the time to definitive results. This has the potential to improve patient management and antimicrobial stewardship. However, the extent of such an impact is yet to be fully assessed. We tested two such assays, the Verigene® System Bloodstream Infection Tests (Nanosphere, Inc., Northbrook, IL, USA) (both Gram-positive and Gram-negative cartridges) and the FilmArray® Blood Culture Identification Panel (BioFire® Diagnostics, Inc., Salt Lake City, UT, USA). We compared their accuracy and speed of organism and resistance gene identification to conventional culture-based methods for 173 positive blood cultures. We also retrospectively determined, for organisms deemed not to be contaminants, the potential impact on antimicrobial prescribing. Both the Verigene® and FilmArray® assays accurately identified organisms, on average, 27.95 and 29.17 h earlier than conventional methods, respectively. There were a significant number of false-positives for Pseudomonas aeruginosa with the FilmArray® assay, which may have been related to contamination of the bioMérieux BacT standard anaerobic blood culture bottles, which the manufacturer has acknowledged. Both panels provided results significantly faster than conventional methods. In our setting, the extent of the potential positive impact on antimicrobial prescribing was modest (9 out of 173 samples). However, this may be an underestimation, since probable contaminants were not included in this analysis. In conclusion, both panels gave accurate results with significantly improved turnaround times.