Predictive Value of Methicillin-Resistant Staphylococcus aureus Nasal Swab PCR Assay for MRSA Pneumonia in Critically Ill Stroke Patients

Abstract

Background:

Ischemic and hemorrhagic strokes are associated with significant morbidity and mortality, with secondary complications such as stroke-associated pneumonia (SAP) contributing to increased mortality rates. Methicillin-resistant Staphylococcus aureus (MRSA) is a key pathogen associated with poor outcomes in this patient population. While MRSA polymerase chain reaction (PCR) nasal swabs have demonstrated high negative predictive value (NPV) in other critically ill populations, their diagnostic utility in stroke patients remains uncharacterized.

Objective:

The objective of this study was to evaluate the diagnostic performance of MRSA PCR nasal swabs in predicting culture-confirmed MRSA pneumonia in critically ill stroke patients.

Methods:

This single-center, retrospective study included adult neurocritical care patients between January 1, 2018, and July 31, 2024, who had confirmed ischemic or hemorrhagic stroke, inclusive of aneurysmal subarachnoid hemorrhage, and underwent both MRSA PCR nasal swab and lower respiratory culture testing. The primary outcome was to define the NPV, positive predictive value (PPV), sensitivity, and specificity of MRSA PCR nasal swabs in predicting culture-confirmed MRSA pneumonia. Secondary outcomes included defining the NPV, PPV, sensitivity, and specificity of methicillin-susceptible Staphylococcus aureus (MSSA) in predicting culture-confirmed MSSA pneumonia.

Results:

Four hundred and thirty-seven patients were screened for inclusion, and of those, 299 were included. The MRSA PCR nasal swab demonstrated an NPV of 100% and a PPV of 34.6% with a sensitivity of 100% and a specificity of 94.1% for culture-confirmed MRSA pneumonia. The MSSA PCR nasal swabs yielded an NPV of 96.6% and a PPV of 32.8% with a specificity of 81.6% and a sensitivity of 75.9%.

Conclusion and Relevance:

The MRSA PCR nasal swabs appear to be a highly reliable diagnostic tool for ruling out MRSA pneumonia in critically ill stroke patients. The 100% NPV and 100% sensitivity demonstrate its potential for allowing safe and timely de-escalation of empiric antibiotic therapy targeting MRSA.