Background:
Septic patients that require ICU level of care are treated empirically with vancomycin. Although this treatment is effective for MRSA infections, prolonged vancomycin exposure can cause nephrotoxicity and antibiotic resistance. A test to identify patients with a low risk for MRSA infection could facilitate early vancomycin discontinuation. In patients presenting with pneumonia, MRSA swabs have been shown to have a negative predictive value (NPV) of 94-97% for the diagnosis of MRSA pneumonia. The correlation between MRSA colonization and infection at other body sites has not been examined in depth.
Methods:
This cohort study utilized a research database that includes all ICU admissions to our facility from 2009 to 2014 that included an admission diagnosis of sepsis. All members of this cohort received a routine MRSA colonization swab at the time of ICU admission. MRSA cases were identified by positive Staphylococcus cultures resistant to oxacillin. Predictive values and likelihood ratios were calculated for MRSA swabs done at admission to the ICU.
Results:
Of the 1116 cases in the database, 121 were Staphylococcus and 41 were MRSA. 24 of the positive MRSA cultures were from blood, 7 from urine and 9 from sputum. The overall positive predictive value (PPV) of MRSA swabs in predicting future MRSA cultures was 8.1% and negative predictive value (NPV) was 99.1% (95% CI 98.1 to 99.6). NPV calculated for blood (NPV 99.6%), urine (NPV 99.9%) and sputum (NPV 99.9%) cultures were similar. The negative likelihood ratio of the MRSA swab test was 0.25 (95% CI 0.13 to 0.49), and the positive likelihood ratio was 2.6 (95% CI 2.21 to 3.06).
Conclusions:
The NPV of 99% for MRSA swabs in this population suggests that critically ill septic patients presenting with a negative MRSA swab are very unlikely to be diagnosed with a MRSA infections during their hospitalization. This high NPV is consistent with other studies and supports the utility of MRSA swabs in identifying patients for early de-escalation of MRSA coverage. In particular, there is sufficient data validating the use of MRSA swabs to drive de-escalation in pneumonia treatment to warrant the implementation of a quality improvement project at the our university hospital. Upon admission, patients with suspected hospital acquired pneumonia are being treated through an orderset which includes a MRSA swab with the initiation of antibiotics. Inpatient pharmacists review the MRSA swab results and recommend discontinuing MRSA coverage if it is negative. The results of this study indicate that such de-escalation may be applicable to other infectious sources as well.