Performance of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus Test before and during High-Volume Clinical Use

Abstract

We evaluated the use of the BD GeneOhm MRSA real-time PCR assay (BD Diagnostics, San Diego, CA) for the detection of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA). The initial evaluation consisted of 403 paired nasal swabs and was done using the specimen preparation provided with the kit and an in-house lysis method that was specifically developed to accommodate large-volume testing using a minimal amount of personnel time. One swab was placed in an achromopeptidase (ACP) lysis solution, and the other was first used for culture and then prepared according to the kit protocol. PCR was performed on both lysates, and results were compared to those for culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the PCR assay were 98%, 96%, 77%, and 99.7% with the kit lysate and 98%, 95%, 75%, and 99.7% with the ACP lysate (P, not significant), respectively. The second evaluation was done after implementation of all-admission surveillance using PCR with ACP lysis and a sampling of 1,107 PCR-negative samples and 215 PCR-positive samples that were confirmed by culture. The results of this sampling showed an NPV of 99.9% and a PPV of 73.5% (prevalence, 6%), consistent with our initial findings. The BD GeneOhm MRSA assay is an accurate and rapid way to detect MRSA nasal colonization. When one is dealing with large specimen numbers, the ACP lysis method offers easier processing without negatively affecting the sensitivity or specificity of the PCR assay.

Rapid Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) in Diverse Clinical Specimens by the BD GeneOhm MRSA Assay and Comparison with Culture

“…In contrast, we performed the PCR assay first followed by culture, which resulted in a sensitivity of merely 84.3%. This may be explained by the use of enrichment broth as the reference method, which yields conceivably a higher sensitivity than does direct plating (17,20,23). Overall sensitivity of PCR for all swabs (n ϭ 1,595) in Amies agar corresponds well to the results reported previously using Stuart's medium (sensitivity ranging from 81% to 92.3%) (3,8,19,22,26).…”

Prediction of Methicillin-Resistant Staphylococcus aureus Involvement in Disease Sites by Concomitant Nasal Sampling

“…We modified the preanalytical specimen processing to facilitate high-volume testing (15). In our center, we have found this assay to have a sensitivity of 98.2% and a specificity of 97.5% (14). Susceptibility testing of all organisms was carried out according to the guidelines of the Clinical Laboratory Standards Institute; clindamycin susceptibilities reflect disk approximation test results (4).…”

Detection of Methicillin-Resistant Staphylococcus aureus by a Duplex Droplet Digital PCR Assay

“…There are several explanations for this discrepancy, such as nonviable organisms that are present at cultivation detected by PCR, the presence of SCCmec variants, or low densities of organisms (24,25). Both the GeneXpert MRSA and GeneOhm assays were found to have false positives due to mecA deletion strains (28,29). The detection of methicillin-resistant coagulase-negative (MRCoN) organisms, such as S. haemolyticus, S. epidermidis, Staphylococcus hominis, or Staphylococcus sciuri, might also account for false positives.…”