Program Schedule

Rapid MRSA PCR on Respiratory Specimens from Ventilated Patients with Suspected Pneumonia: A Potential Tool for Antimicrobial Stewardship

Session: Poster Abstract Session: Antibiotic Stewardship
Thursday, October 9, 2014
Room: The Pennsylvania Convention Center: IDExpo Hall BC
  • MRSA Xpert IDWeek 2014 poster v1.3.pdf (277.0 kB)
  • Background: Methicillin-resistant Staphylococcus aureus (MRSA) infection is an important cause of ventilator-associated pneumonia.  As a result, empiric therapy often includes anti-staphylococcal agents. Our objective was to evaluate the GeneXpert MRSA/SA SSTI Assay (Cepheid, Sunnyvale, CA) for use in lower respiratory tract (LRT) specimens for rapid MRSA detection as a tool in antimicrobial stewardship efforts.

    Methods: For the validation of the assay, we included laboratory-derived (“spiked”) bronchoalveolar lavage (BAL) specimens with known quantities of MRSA (SCCmec II and IV; 102 - 105 CFU/mL) and 30 banked LRT samples. For the clinical phase, we determined if LRT samples submitted to the microbiology lab met criteria for suspected pneumonia and were collected from ventilated patients. Comparator standard-of care culture results and antibiotic utilization information were collected. Antibiotic days for vancomycin and linezolid were calculated.

    Results: The limit of detection for MRSA in the spiked BAL samples was 103 CFU/ml. The assay correctly detected MRSA in 9/9 frozen samples and excluded MRSA in 21/21 samples with other organisms (sensitivity 100%, specificity 100%). We screened 310 LRT specimens; 100 met study criteria. Ten samples tested positive for MRSA with rapid PCR, while 6 were positive in routine cultures. Rapid PCR correctly detected 5/6 positive and 89/94 negative MRSA specimens for a sensitivity of 83.3% (95% CI: 36.1-97.2%) and specificity of 94.7% (95% CI: 88-98.2%) with a negative predictive value of 98.9% (95% CI: 93.9-99.8%). A total of 748 vancomycin and 305 linezolid antibiotic days were associated with the enrolled specimens. Vancomycin and linezolid utilization would decrease by 68.4% and 83%, respectively, if they were discontinued 1 day after negative rapid PCR results.

    Conclusion: A rapid MRSA PCR test performed well against the gold standard in respiratory samples from ventilated patients with suspected pneumonia. Its implementation has the potential of reducing empiric vancomycin and linezolid utilization.

    Sergio E. Trevino, MD1, Morgan a. Pence, PhD2, Jonas Marschall, MD1,3, Marin H. Kollef, MD4, Hilary M. Babcock, MD, MPH1 and Carey-Ann D. Burnham, PhD5, (1)Division of Infectious Diseases, Department of Medicine, Washington University School of Medicine, St. Louis, MO, (2)Pathology and Immunology, Washington University School of Medicine, Saint Louis, MO, (3)Department of Infectious Diseases, Bern University Hospital and University of Bern, Bern, Switzerland, (4)Pulmonary and Critical Care Medicine, Washington University School of Medicine, St. Louis, MO, (5)Pediatrics, Pathology and Immunology, Washington University School of Medicine, St Louis, MO


    S. E. Trevino, None

    M. A. Pence, None

    J. Marschall, None

    M. H. Kollef, None

    H. M. Babcock, None

    C. A. D. Burnham, Cepheid: Investigator, Research support

    Findings in the abstracts are embargoed until 12:01 a.m. EDT, Oct. 8th with the exception of research findings presented at the IDWeek press conferences.

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