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Park, Jang, Sung, Kim, Kim, and Park: Performance Evaluation of BD GeneOhm MRSA PCR Assay for Detection of Nasal Colonization of Methicillin-Resistant Staphylococcus aureus at Endemic Intensive Care Units
Original Article

Korean J Leg Med 2009;29(5):439-447.

Published online: 14 January 2009

DOI: https://doi.org/10.3343/kjlm.2009.29.5.439

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

Sang Hyuk Park, M.D.1, Yoon Ha Jang, M.D.1, Heungsup Sung, M.D.1, Mi-Na Kim, M.D.1, Jae Suk Kim, M.D.2, Yeon Joon Park, M.D.3

1Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea

2Department of Laboratory Medicine, Hallym University College of Medicine, Seoul, Korea

3Department of Laboratory Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea

Corresponding author: Mi-Na Kim, M.D. Department of Laboratory Medicine, Asan Medical Center and University of Ulsan College of Medicine, 388-1 Pungnap-2dong, Songpa-gu, Seoul 138-736, Korea Tel: +82-2-3010-4511, Fax: +82-2-478-0884 E-mail: mnkim@amc.seoul.kr

      Revised 11 March 200917 July 2009       Accepted 7 August 2009

Copyright © 2009 Korean Society for Legal Medicine

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background:

The BD GeneOhm MRSA PCR assay (Becton Dickinson, USA) is a qualitative realtime 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 μL 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.

Keywords: BD GeneOhm, MRSA, Nasal colonization, Performance

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Table 1.
Clinical characteristics of 190 study patients
  Surveillance-negative Surveillance-positive P value
Number of patients 97 (51.1%) 93 (48.9%)  
Age (yr, mean±SD) 35.8±3.4 48.1±3.1 <0.001
Sex (male:female) 55:42 67:26 0.027
Hospital stay (days) 41.8±3.7 138.9±51.6 0.008
MRSA infections      
Pneumonia 0 (0.0%) 20 (21.5%) <0.001
Bacteremia 0 (0.0%) 7 (7.5%) 0.006
Wound infection 0 (0.0%) 3 (3.2%) 0.075
Infective endocarditis 0 (0.0%) 2 (2.2%) 0.147
Total 0(0.0%) 32(34.4%) <0.001
Antimicrobial treatments      
Vancomycin 45 (46.4%) 72 (77.4%) <0.001
Linezolid 0 (0.0%) 2 (2.2%) 0.147
Teicoplanin 4 (4.1%) 16 (17.2%) 0.003
Total 45 (46.4%) 72 (77.4%) <0.001
Table 2.
Results of three different MRSA surveillance tests with the results of previous and follow-up surveillance cultures for the specimens showing a discrepancy between the three tests
Results with N of specimens (Patients) Previous surveillance Follow-up surveillance
TSBS GeneOhm MRSA MRSA Select N Tested N Positive N Negative N Tested N Positive N Negative
Positive Positive Positive 81 (55) NI NI NI NI NI NI
Negative Negative Negative 144 (70) NI NI NI NI NI NI
Negative Positive Positive 2 (2) 2 2 0 2 1 1
Positive Positive Negative 10 (10) 10 5 5 7 5 2
Negative Positive Negative 32 (31) 31 11 20 25 10 15
Positive Negative Positive 2 (2) 2 2 0 2 2 0
Negative Negative Positive 1 (1) 1 1 0 1 1 0
Positive Negative Negative 8 (8) 8 8 0 8 8 0
Negative Unresolved Negative 8 (7) 7 0 7 5 0 5
Positive Unresolved Negative 5 (4) 4 1 3 1 0 1

Abbreviations: NI, not investigated.

Table 3.
Comparison of BD GeneOhm MRSA PCR assay and MRSASelect to the reference results
  Reference results∗ Sensitivity Specificity Positive predictive value Negative predictive value
N Positive N Negative Total
GeneOhm MRSA              
Positive 91 34 125 85.8% 77.5% 72.8% 93.5%
Negative 10 145 155 (0.79-0.92)† (0.72-0.83)† (0.65-0.81)† (0.90-0.97)†
Unresolved 5 8 13        
Total 106 187 293        
MRSASelect              
Positive 83 3 86 78.3% 98.4% 96.5% 88.9%
Negative 23 184 207 (0.70-0.86)† (0.97-1.00)† (0.93-1.00)† (0.85-0.93)†
Total 106 187 293        

∗ Results from 6.5% NaCl-tryptic soy broth enrichment followed by a subculture with MRSASelect (TSBS);

† CI: 95% confidence interval.

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