Evaluation of the BD GeneOhm MRSA Real-time PCR Assay for Detection of Nasal Colonization by MRSA / 대한임상미생물학회지

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) is a major nasocomial pathogen. The active surveillance of MRSA is essential to limit its transmission. The BD GeneOhm MRSA real-time PCR assay (Becton Dickinson Diagnostics, San Diego, USA) has been recently developed and used for same-day MRSA detection directly from nasal swab specimens. The authors of the present study compared GeneOhm MRSA PCR with culture methods to evaluate its diagnostic performance for MRSA active surveillance. METHODS: The present study was conducted on patients admitted to the ICU for six months. A total of 371 nasal swab specimens were obtained from patients at admission day and at the seven-day follow-up. The swab was streaked onto culture media, and presumptive S. aureus colonies were confirmed as MRSA using the BD Phoenix automated microbiology system (Becton Dickinson Diagnostic Systems, Sparks, USA). In addition, GeneOhm MRSA PCR was performed. For discrepant results between Gene-Ohm MRSA PCR and culture, the enrichment broth culture method was performed. RESULTS: There were 34 samples with discrepant results between the GeneOhm MRSA PCR and culture. The overall agreement was 90.7%. For the detection of MRSA, the GeneOhm MRSA PCR was 96.8% sensitive and 86.3% specific, with positive and negative predictive values of 83.9% and 97.3%, respectively. CONCLUSION: Identification of MRSA-colonized patients was achieved in as little as two hours, and the high negative predictive value of GeneOhm MRSA PCR suggests that the assay is a rapid method for the identification of persons who are not colonized with MRSA. However, due to the low positive predictive value, GeneOhm MRSA PCR combined with enrichment culture in cases of positive GeneOhm MRSA PCR is potentially useful for active MRSA surveillance activities.

Performance Evaluation of BD GeneOhm MRSA PCR Assay for Detection of Nasal Colonization of Methicillin-Resistant Staphylococcus aureus at Endemic Intensive Care Units / 대한진단검사의학회지

BACKGROUND: The BD GeneOhm MRSA PCR assay (Becton Dickinson, USA) is a qualitative real-time PCR test for rapid detection of nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA). We evaluated the performance of BD GeneOhm MRSA PCR assay versus MRSASelect (Bio-Rad, France) and broth enrichment cultures for detection of MRSA from nasal swabs. METHODS: From August 2008 to January 2009, 295 nasal swabs were taken from patients in intensive care units and transported to the laboratory with BD CultureSwab Liquid Stuart Single Swab (Becton Dickinson, USA). The swabs were inoculated onto MRSASelect first and then suspended into GeneOhm sample buffer: 100 microliter of the suspension was inoculated into 6.5% NaCl-tryptic soy broth (Becton Dickinson, USA), which was subcultured on MRSASelect after overnight incubation (TSBS). Performances of GeneOhm MRSA and MRSASelect were compared to TSBS. RESULTS: With GeneOhm MRSA, 125 swabs (44.6%) were positive for MRSA, 13 (4.4%) were unresolved, and 2 were not determined. With MRSASelect and TSBS 86 (29.4%) and 106 swabs (36.2%), respectively, were positive. The sensitivity, specificity, and positive and negative predictive value of GeneOhm MRSA were 85.8%, 77.5%, and 72.8% and 93.5%, respectively, and corresponding values for MRSASelect were 78.3%, 94.8%, and 96.5% and 88.9%. Of the 33 patients whose 34 specimens were found false positive in GeneOhm MRSA, 23 patients were MRSA-positive either previously or subsequently to this study. All of the 10 patients with false-negative specimens in GeneOhm MRSA PCR assay were previously MRSA or methicilln-resistant coagulase negative staphylococci (MRCNS)-positive and were treated for MRSA, but they became MRSA-positive after 1 to 4 negative surveillance cultures. CONCLUSIONS: GeneOhm MRSA PCR assay showed a relatively high negative predictive value. However, its low specificity and frequent occurrence of unresolved results would be problematic in the endemic areas with a high prevalence of MRSA.