Original Research

Clinical Utility of Methicillin-Resistant Staphylococcus aureus Polymerase Chain Reaction Nasal Swab Testing in Lower Respiratory Tract Infections



From the Hospital of Central Connecticut, New Britain, CT (Dr. Caulfield and Dr. Shepard); Hartford Hospital, Hartford, CT (Dr. Linder and Dr. Dempsey); and the Hartford HealthCare Research Program, Hartford, CT (Dr. O’Sullivan).


  • Objective: To assess the utility of methicillin-resistant Staphylococcus aureus (MRSA) polymerase chain reaction (PCR) nasal swab testing in patients with lower respiratory tract infections (LRTI).
  • Design and setting: Multicenter, retrospective, electronic chart review conducted within the Hartford HealthCare system.
  • Participants: Patients who were treated for LRTIs at the Hospital of Central Connecticut or Hartford Hospital between July 1, 2018, and June 30, 2019.
  • Measurements: The primary outcome was anti-MRSA days of therapy (DOT) in patients who underwent MRSA PCR testing versus those who did not. In a subgroup analysis, we compared anti-MRSA DOT among patients with appropriate versus inappropriate utilization of the MRSA PCR test.
  • Results: Of the 319 patients treated for LRTIs, 155 (48.6%) had a MRSA PCR ordered, and appropriate utilization occurred in 94 (60.6%) of these patients. Anti-MRSA DOT in the MRSA PCR group (n = 155) was shorter than in the group that did not undergo MRSA PCR testing (n = 164), but this difference did not reach statistical significance (1.68 days [interquartile range {IQR}, 0.80-2.74] vs 1.86 days [IQR, 0.56-3.33], P = 0.458). In the subgroup analysis, anti-MRSA DOT was significantly shorter in the MRSA PCR group with appropriate utilization compared to the inappropriate utilization group (1.16 [IQR, 0.44-1.88] vs 2.68 [IQR, 1.75-3.76], P < 0.001)
  • Conclusion: Appropriate utilization of MRSA PCR nasal swab testing can reduce DOT in patients with LRTI. Further education is necessary to expand the appropriate use of the MRSA PCR test across our health system.

Keywords: MRSA; LRTI; pneumonia; antimicrobial stewardship; antibiotic resistance.

More than 300,000 patients were hospitalized with methicillin-resistant Staphylococcus aureus (MRSA) infections in the United States in 2017, and at least 10,000 of these cases resulted in mortality.1 While MRSA infections overall are decreasing, it is crucial to continue to employ antimicrobial stewardship tactics to keep these infections at bay. Recently, strains of S. aureus have become resistant to vancomycin, making this bacterium even more difficult to treat.2

A novel tactic in antimicrobial stewardship involves the use of MRSA polymerase chain reaction (PCR) nasal swab testing to rule out the presence of MRSA in patients with lower respiratory tract infections (LRTI). If used appropriately, this approach may decrease the number of days patients are treated with anti-MRSA antimicrobials. Waiting for cultures to speciate can take up to 72 hours,3 meaning that patients may be exposed to 3 days of unnecessary broad-spectrum antibiotics. Results of MRSA PCR assay of nasal swab specimens can be available in 1 to 2 hours,4 allowing for more rapid de-escalation of therapy. Numerous studies have shown that this test has a negative predictive value (NPV) greater than 95%, indicating that a negative nasal swab result may be useful to guide de-escalation of antibiotic therapy.5-8 The purpose of this study was to assess the utility of MRSA PCR nasal swab testing in patients with LRTI throughout the Hartford HealthCare system.



This study was a multicenter, retrospective, electronic chart review. It was approved by the Hartford HealthCare Institutional Review Board (HHC-2019-0169).

Selection of Participants

Patients were identified through electronic medical record reports based on ICD-10 codes. Records were categorized into 2 groups: patients who received a MRSA PCR nasal swab testing and patients who did not. Patients who received the MRSA PCR were further categorized by appropriate or inappropriate utilization. Appropriate utilization of the MRSA PCR was defined as MRSA PCR ordered within 48 hours of a new vancomycin or linezolid order, and anti-MRSA therapy discontinued within 24 hours of a negative result. Inappropriate utilization of the MRSA PCR was defined as MRSA PCR ordered more than 48 hours after a new vancomycin or linezolid order, or continuation of anti-MRSA therapy despite a negative MRSA PCR and no other evidence of a MRSA infection.


Next Article: