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Internal Medicine


Comparative Detection Of Airway MRSA In Patients With Community-Acquired Pneumonia (CAP)

Hiromichi Park, DO

Providence Portland Medical Center

Portland, OR

Additional Authors: Shirin Ferdosian Najafabadi; Lian Wang, PhD; David Gilbert, MD, MACP

Introduction: Vancomycin is often included in the empiric therapy of CAP to ensure activity against MRSA. The current gold standard for detection of MRSA in the airway is a nasal swab PCR. The FilmArray sputum pneumonia panel includes PCR probes for MRSA. This study compares the detection performance of the nasal swab versus the sputum PCR detection of MRSA. Clinically, the absence of airway-detectable MRSA allows cessation of empiric Vancomycin.

Methods: 585 patients with Community Acquired Pneumonia (CAP) were enrolled to compare pathogen detection with a “bundle” of tests versus the new 33 target FilmArray sputum pneumonia panel. Of the 585 patients, 112 patients were evaluable for comparative detection of S. aureus via blood and sputum culture, sputum FilmArray pneumonia panel and nasal swab PCR.

Results: The FilmArray pneumonia panel sampled from sputum detected 69 cases representing 62.2% of total evaluable cases. Nasal swab PCR detected 92 cases representing 82% of total cases. P value was 0.004 between tests. Sputum PCR had a sensitivity rate of 63.9% with a negative predictive value of 94.7% when nasal PCR was considered as the gold standard for MRSA detection. Conversely the nasal PCR had a sensitivity of 85.2% with negative predictive value of 98.3% when sputum PCR is gold standard. Among cases that were simultaneously detected by nasal and sputum PCR, species (MSSA and MRSA) match rate was 52/56 (92.3%).

Discussion: Nasal swab PCR testing had significantly higher sensitivity than sputum PCR in detection of S. aureus (both MSSA and MRSA). Of clinical import, a negative nasal PCR for MRSA supports discontinuation of empiric Vancomycin Therapy. Conversely, the 20% lower frequency of MRSA detection with the sputum PCR creates uncertainty in decisions to discontinue Vancomycin therapy.

Conclusions: Nasal PCR for S. aureus is more sensitive than sputum PCR for both MSSA and MRSA. In a critically ill patient with influenza and elevated serum Procalcitonin level, the most sensitive method to detect the presence of MRSA is a nasal swab PCR.


Internal Medicine


Graduate Medical Education

Conference / Event Name

Academic Achievement Day, 2020


Providence Portland Medical Center, Internal Medicine Residency, Portland, Oregon

Comparative Detection Of Airway MRSA In Patients With Community-Acquired Pneumonia (CAP)