2026 Southeastern Residency Conference

Correlation of Methicillin-Resistant Staphylococcus Aureus Polymerase Chain Reaction Nasal Swab in Empyema
Elliott Wilch; Sarah Frye; Martin Gordon; Cragin Currence

Background: Empyema or pyothorax is defined by the presence of purulent exudate in the pleural space and is a life-threatening infectious condition. The most common cause of empyema is bacterial pneumonia and its resulting parapneumonic effusion. Among these patients, 5 to 10% will develop empyema and 30% will require surgical drainage. The American Association of Thoracic Surgery (AATS) Guidelines for the Management of Empyema recommend covering for methicillin-resistant Staphylococcus aureus (MRSA) in patients with hospital acquired empyema as well as those with post-surgical infections. Both the Infectious Disease Society of America (IDSA) and the AATS guidelines do not provide any guidance on de-escalation of antibiotics before the availability of definitive cultures. This contributes to extended durations of anti-MRSA antimicrobials, potentially leading to antimicrobial resistance, Clostridium difficile infections, increased lengths of stay, and increased costs. The clinical utility of MRSA polymerase chain reaction (PCR) nasal swab is well established for antibiotic de-escalation in pneumonia, with multiple studies showing that an MRSA PCR nasal swab has an excellent negative predictive value (NPV) of up to 98%. These studies have demonstrated that the MRSA PCR nasal swab can be a tool used in antimicrobial stewardship to avoid unnecessary anti-MRSA antibiotics as empiric therapies. While the MRSA PCR nasal swab has demonstrated value in pneumonia, very few studies exist assessing its use in infections such as empyema. The following study was conducted to assess the correlation of MRSA PCR nasal swab in patients with empyema.
Methods: This was a single-center, retrospective cohort study assessing the correlation of MRSA PCR nasal swab in empyema. Adult patients with the diagnosis of empyema who had an MRSA PCR obtained during admission were included in the study. Patients were excluded if there were no definitive cultures collected. The primary outcome for the study was the correlation between the MRSA PCR nasal swab and definitive cultures utilizing NPV in patients with empyema. Secondary outcomes included the correlation between the MRSA PCR nasal swab and definitive cultures utilizing specificity, sensitivity, and positive predictive value in patients with empyema. Antimicrobial agent, duration, and time between culture collection and initiation of antibiotics were also analyzed in the study.
Results: Among the 355 patients initially reviewed, 118 did not meet the inclusion criteria, most commonly due to a lack of culture collection. There were 237 patients included in the final analysis. The primary outcome of negative predictive value was 96%. The secondary outcomes of positive predictive value, sensitivity, and specificity were 45%, 55%, and 94.5% respectively.
Conclusion: When examining the utility of the MRSA PCR in empyema, the NPV and specificity were 96% and 94.5% respectively. This study demonstrates that the MRSA PCR nasal swab assay has the potential to be a vital tool in de-escalating antimicrobial therapy in empyema. Utilizing this tool as a means of de-escalation has multiple potential benefits including limiting MRSA antimicrobials and their associated side effects, reducing rates of resistance, and possibly leading to decreased costs for the patient and the healthcare system. While these results are promising, there are several limitations to this study, primarily its retrospective nature and its limited sample size. Future prospective studies are needed to generalize the findings in larger patient populations.