(656) Clinical Utility of Nasal MRSA Polymerase Chain Reaction in Patients With Diabetic Foot Infections

Introduction: As the prevalence of diabetes increases worldwide, so does the incidence of diabetic foot infections. A potential tool for antibiotic de-escalation in these patients is nasal MRSA polymerase chain reaction (PCR) screening. This study aimed to provide evidence to determine the clinical utility of nasal MRSA PCR screening to predict the presence or absence of MRSA in cultures for patients with diabetic foot infections.

Methods: In this retrospective chart review from a multi-hospital health system, nasal MRSA PCR results were paired with culture results to determine PPV, NPV, sensitivity, and specificity. Patients were required to have a diabetic foot infection diagnosis during hospitalization, have a finalized MRSA PCR during admission, and finalized culture results within 7 days of the MRSA PCR.

Results: 307 patient admissions were reviewed with 282 meeting inclusion criteria. The PPV of nasal MRSA PCR in diabetic foot infections was 74% and NPV was 82.8%. Sensitivity and specificity were 48.1% and 93.7%, respectively. 182 patients met the definition for osteomyelitis while 100 patients did not have osteomyelitis. There was no statistically significant difference between patients with and without osteomyelitis with PPV (p = 0.93) , NPV (p = 0.67), sensitivity (p = 0.95), or specificity (p = 0.73). The prevalence of MRSA was 27.3% for the total patient population.

Conclusions: The results of this study suggest a negative MRSA PCR nasal swab obtained within 7 days of a culture has a low NPV for MRSA in diabetic foot infections, risking inappropriate antibiotic de-escalation in approximately 17% of patients. This data suggests there is low clinical utility for the use of nasal MRSA PCR in diabetic foot infections.