Friday, February 8, 2013

Controlled Multicenter Evaluation of a Bacteriophage Based Method for the Rapid Detection of Staphylococcusaureus in Positive Blood Cultures.

Controlled Multicenter Evaluation of a Bacteriophage Based Method for the Rapid Detection of Staphylococcusaureus in Positive Blood Cultures.

Feb 2013


UMDNJ-Robert Wood Johnson Medical School, 1 Robert Wood Johnson Place, New Brunswick, NJ 08901.


Staphylococci are a frequent cause of bloodstream infections (BSIs). Appropriate antibiotic treatment for BSIs may be delayed because conventional laboratory testing methods take 48-72 hours to identify and characterize isolates from positive blood cultures. We evaluated a novel assay based on bacteriophage amplification that identifies S. aureus and differentiates between methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA, respectively) in samples taken directly from signal positive BACTEC™ blood culture bottles within 24 hours of positive signal, with results available within 5 hours. The performance of the MicroPhage KeyPath™ MRSA/MSSA Blood Culture Test was compared to conventional identification and susceptibility testing methods. At four sites, we collectively tested a total of 1165 specimens of which 1116 were included in our analysis. Compared to standard methods, the KeyPath™ MRSA/MSSA Blood Culture Test demonstrated a sensitivity, specificity, positive predictive value and negative predictive value of 91.8%, 98.3%, 96.3% and 96.1%, respectively for correctly identifying S. aureus. Of those correctly identified as S. aureus (n=334), 99.1% were correctly categorized as either MSSA or MRSA. Analysis of a subset of the data revealed that the KeyPath™ MRSA/MSSA Blood Culture Test delivered results a median of 30 hours sooner than conventional methods (a median of 46.9 hours vs a median of 16.9 hours). Although the sensitivity of the test in detecting S. aureus-positive samples is not high, its accuracy in determining methicillin resistance and susceptibility among positives is very high. These characteristics may enable earlier implementation of appropriate antibiotic treatment for many S. aureus BSI patients. (Subsets of these results were presented at the 2010 ICAAC meeting in Boston, MA and the 2011 ASM meeting in New Orleans).