Background: Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of both community and hospital acquired infections. According to CDC, MRSA is responsible for 70,000 severe infections and 9,000 deaths per year. The MRSA nasal PCR (MRSA PCR) is a screening test for MRSA colonization in the nares. It has a sensitivity of about 67.4% and specificity of 81.2% with a positive predictive value (PPV) of 24.6% and negative predictive value (NPV) of 96.5%. IDSA does not provide specific guidelines for routine MRSA screening, thus the implementation of screening protocols varies across healthcare settings. The MRSA PCR result turnaround is typically 2-6 hours. Given its high NPV, MRSA PCR testing could potentially guide the de-escalation of MRSA targeted antibiotic therapy. However, there is a need for more evidence-based data to determine the most beneficial utilization of MRSA PCR testing.

Methods: We performed a retrospective study of all patients who received MRSA PCR at University of Mississippi Medical Center from January 3, 2013 to December 31, 2019. Patient Cohort Explorer was used to obtain de-identified patient data from EPIC. We obtained the number of encounters and patients on whom the MRSA PCR was performed.

Results: MRSA PCR was ordered on 40,806 times on 32,686 patients during 37,630 hospital encounters between 2013 and 2019. MRSA PCR was positive in 4,599 times in 4015 patients and negative 36,207 times in 28,671 patients. Total percentage of positive MRSA PCRs is 11.27% and negative MRSA PCRs is 88.73%. The percentage of positive MRSA PCRs is 10.55% to 14.18% from 2013 to 2019. Female, male ratio for positive MRSA PCRs is 0.79 and negative MRSA PCRs is 0.76 (p value 0.45). The median age for a positive MRSA PCR is 46 while it is 49 for negative MRSA PCR. The proportion of African American and Caucasian is 53% and 44% in positive MRSA PCRs and 55% and 42 % in negative MRSA PCRs. The ratio for alive to deceased patients for positive MRSA PCR is 3.37 and for negative patients is 4.26 (p value < 0.005). After hospitalization, 62% of the positive MRSA PCR patients are discharged home and 13% expired. Discharge to home is higher at 69% for negative patients with a lower 10% mortality (p value <0.005). The median length of stay is 6 days for both positive and negative MRSA PCR patients.

Conclusions: Our study describes the epidemiological characters and rates of positivity at UMMC and has one the largest single institution sample size for MRSA PCR testing. Limited data is available on outcomes with MRSA colonization based on PCR testing. Our study shows higher mortality and lower discharge to home rates with patients who are positive MRSA PCR.