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Journal of Clinical Microbiology, April 2006, p. 1604-1605, Vol. 44, No. 4
0095-1137/06/$08.00+0     doi:10.1128/JCM.44.4.1604-1605.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

Rapid Molecular Detection of Methicillin-Resistant Staphylococcus aureus


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LETTER
 
Two recent studies using conventional screening methods have demonstrated significant reductions in wound infections due to methicillin-resistant Staphylococcus aureus (MRSA) following use of preoperative topical suppression in carriers (3, 5). Analysis of wound infection surveillance in this hospital suggests that each MRSA surgical wound infection costs an average of £4,200 ($7,500) in addition to that of routine care (6).

Over 90% of these costs relate to the prolonged stay in the hospital. Conventional screening takes up to 3 days, during which time staff can unwittingly spread MRSA from carriers to others (1). Rapid detection of MRSA carriage should therefore contribute to the prevention of transmission. However, most of the currently available rapid techniques cannot differentiate between pure MRSA and a mixture of methicillin-sensitive Staphylococcus aureus and methicillin-resistant coagulase-negative staphylococci.

A new test (IDI-MRSA; GeneOhm Sciences) claims to reliably detect MRSA in nasal swabs on the same day as receipt. This is achieved by target amplification with primers and probes designed to detect the right-hand region of the mecA cassette and the neighboring orfX gene. The amplified targets are then detected using fluorescent molecular beacon technology. An internal control is included to detect the presence of moieties inhibitory to the PCR.

Of 1,879 samples tested, multiple samples from the same site in the same patient were excluded, resulting in 1,240 patients and 1,211 resolved nasal specimens (1,217 with direct culture on mannitol salt agar plates containing 4 mg/liter oxacillin and 1,211 with an IDI test result). Resolved results are those where discrepant results were further tested using an enrichment protocol of overnight incubation of the original swab at 35°C in nutrient broth supplemented with 4% NaCl and subculture onto appropriate solid media for 24 to 48 h at 35°C. Currently, preenrichment of samples before carrying out the PCR is not performed on routine screening samples as this would add unacceptable delay and affect "same-day" turnaround for the majority of samples.

Overall the prevalence of positive results for MRSA in nasal swabs was 4.8% and 7.4% for culture and IDI tests, respectively. After enrichment, the resolved prevalence was 6.6%. The results for the performance of the IDI test are presented in Table 1.


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  		TABLE 1. Results for the performance of the IDI testa

We have also performed the IDI-MRSA test on 340 screening swabs from other sites and have shown the method to give similar results (not shown here).

When tested against culture for MRSA in 288 patients in another study, this method achieved a similar sensitivity of 91.7%, a specificity of 93.5%, and positive and negative predictive values of 82.5% and 97.1%, respectively (4). The manufacturer's product insert (DMR03-S5-M04) reports a sensi-tivity of 92.5% and a specificity of 96.4% versus culture in 786 nasal specimens. The same method detected 98.7% of a series of 1,657 MRSA strains in another study (2). Although 4.6% of 569 methicillin-sensitive S. aureus isolates were misidentified, none of 286 coagulase-negative isolates were picked out. In 18 nasal swabs spiked with MRSA, the detection limit was reported as 25 CFU. Results are available in less than 3 hours, allowing for easier and more flexible screening at preassessment clinics and the prescription of a topical suppression protocol before admission for surgery. In practice, specimens are processed in daily batches and not out of office hours. Nevertheless, this short turnaround time is especially useful for patients who are admitted as emergency cases, as measures relating to MRSA colonization can often be invoked before the patient undergoes surgery.

We now consider the logistics of specimen acquisition, transport, and action subsequent to the test result a larger obstacle to overcome than the test itself.


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REFERENCES
 
    1
  1. Cepeda, J. A., T. Whitehouse, B. Cooper, J. Hails, K. Jones, F. Kwaku, L. Taylor, S. Hayman, B. Cookson, S. Shaw, C. Kibbler, M. Singer, G. Bellingan, and A. P. Wilson. 2005. Isolation of patients in single rooms or cohorts to reduce spread of MRSA in intensive-care units: prospective two-centre study. Lancet 365:295-304.[Medline]
    2. 2
  2. Huletsky, A., R. Giroux, V. Rossbach, M. Gagnon, M. Vaillancourt, M. Bernier, F. Gagnon, K. Truchon, M. Bastien, F. J. Picard, A. van Belkum, M. Ouellette, P. H. Roy, and M. G. Bergeron. 2004. New real-time PCR assay for rapid detection of methicillin-resistant Staphylococcus aureus directly from specimens containing a mixture of staphylococci. J. Clin. Microbiol. 42:1875-1884.[Abstract/Free Full Text]
    3. 3
  3. Schelenz, S., D. Tucker, C. Georgeu, S. Daly, M. Hill, J. Roxburgh, and G. L. French. 2005. Significant reduction of endemic MRSA acquisition and infection in cardiothoracic patients by means of an enhanced targeted infection control programme. J. Hosp. Infect. 60:104-110.[Medline]
    4. 4
  4. Warren, D. K., R. S. Liao, L. R. Merz, M. Eveland, and W. M. Dunne, Jr. 2004. Detection of methicillin-resistant Staphylococcus aureus directly from nasal swab specimens by a real-time PCR assay. J. Clin. Microbiol. 42:5578-5581.[Abstract/Free Full Text]
    5. 5
  5. Wilcox, M. H., J. Hall, H. Pike, P. A. Templeton, W. N. Fawley, P. Parnell, and P. Verity. 2003. Use of perioperative mupirocin to prevent methicillin-resistant Staphylococcus aureus (MRSA) orthopaedic surgical site infections. J. Hosp. Infect. 54:196-201.[CrossRef][Medline]
    6. 6
  6. Wilson, A. P. R., B. Hodgson, M. Liu, D. Plummer, I. Taylor, J. Roberts, M. Jit, and C. Sherlaw-Johnson. Wound surveillance with post discharge follow-up and feedback in a UK teaching hospital. Br. J. Surg., in press.
M. W. D. Wren*
Caroline Carder
P. G. Coen
V. Gant
A. P. R. Wilson
Department of Clinical Microbiology
University College Hospitals NHS Foundation Trust
The Windeyer Institute of Medical Sciences
46, Cleveland Street
London W1T 4JF, United Kingdom

* Phone: 44 207 380 9519, Fax: 44 207 636 6482, E-mail: mike.wren{at}uclh.nhs.uk

Journal of Clinical Microbiology, April 2006, p. 1604-1605, Vol. 44, No. 4
0095-1137/06/$08.00+0     doi:10.1128/JCM.44.4.1604-1605.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Wang, X.-P., Ginocchio, C. C. (2009). Automation of the BD GeneOhm Methicillin-Resistant Staphylococcus aureus Assay for High-Throughput Screening of Nasal Swab Specimens. J. Clin. Microbiol. 47: 1546-1548 [Abstract] [Full Text]  
  • Paule, S. M., Mehta, M., Hacek, D. M., Gonzalzles, T.-M., Robicsek, A., Peterson, L. R. (2009). Chromogenic Media vs Real-Time PCR for Nasal Surveillance of Methicillin-Resistant Staphylococcus aureus: Impact on Detection of MRSA-Positive Persons. Am J Clin Pathol 131: 532-539 [Abstract] [Full Text]  
  • Krishna, B V S, Smith, M, McIndeor, A, Gibb, A P, Dave, J (2008). Evaluation of Chromogenic MRSA medium, MRSASelect and Oxacillin Resistance Screening Agar for the detection of methicillin-resistant Staphylococcus aureus. J. Clin. Pathol. 61: 841-843 [Abstract] [Full Text]  
  • Boyce, J. M., Havill, N. L. (2008). Comparison of BD GeneOhm Methicillin-Resistant Staphylococcus aureus (MRSA) PCR versus the CHROMagar MRSA Assay for Screening Patients for the Presence of MRSA Strains. J. Clin. Microbiol. 46: 350-351 [Abstract] [Full Text]  
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