Utilizing Nanosphere's Verigene® Technology to Assist with Possible Rapid Pharmacologic De-escalation of Antimicrobial Therapy In A University Hospital Setting

Background: Rapid diagnostic testing is in the clinical microbiology laboratory continues to grow rapidly. We evaluted the utility of the Nanosphere Verigene® system for Gram-positive and Gram-negative bacteria to enable faster de-escalation for bloodstream infections due to either Enterobactericeae (ENT) or Gram-positive (GP) bacteria.

Methods: All positive blood cultures from July 2014 - June 2015 were obtained from our clinical microbiology laboratory systems. Duplicate isolates were removed as well as all polymicrobial cultures. Isolates were identified by the Phoenix® and Vergene® systems. Those blood cultures undergoing testing by both sysems were compared for appropriate identification. Any isolate not correctly identified by both systems were labeled as mismatched. Susceptibility data for matched pairs was evaluated for common beta lactams used to treat gram-negative and -positive infections. Matched pairs with susceptibility rates >90% were deemed appropriate for rapid de-escalation.

Results: Overall, there were 1638 positive blood cultures (1159 GP and 479 ENT) in the study period with 705 cultures (449 GP; 256 ENT) having both rapid diagnostic results and in vitro susceptibility testing performed. The overall agreement between Nanosphere® and Phoenix® testing was 96% with no differences noted for GP or ENT.The most common ENT were E. coli (145/256 [57%]) and K. pneumoniae (65/256 [25%]), The only resistance mechanism noted by Nanosphere was CTX-M isolated in 14/195 (9.7%) E. coli. There were no carbapenem resistant ENT isolated during this study. The highest identification mismatch occurred with K. pneumoinae (8/65, 12.3%) followed by K. oxytoca (1/16, 6.3%) and E. coli (2/145, 1.4%). Of the GP, S. aureus is by far the most common (75%) followed by E. faecalis (15%). E. faecium is the most resistant (71%) followed by S. aureus (52% MRSA) and then only 3% E. faecalis.

Conclusion: Rapid diagnositic identification using the Nanosphere Verigene® system allows for de-escalation to occur for GP and ENT at our academic medical center.