Clinical utility of methicillin-resistant Staphylococcus aureus nasal ... - BMC Infectious Diseases

This single-center, retrospective, quasi-experimental study assessed the effect of MRSA nasal PCR testing on MRSA-targeted antimicrobial use and clinical outcomes in patients with DFI with or without OM. Although the current IDSA DFI guidelines only recommend empiric MRSA-targeted therapy when there is high local prevalence or in cases of severe infection, there is no recommendation for de-escalation, which may lead to an overutilization of anti-MRSA [2]. Based on previous internal data, we chose to primarily assess what effect MRSA nasal PCR would have on anti-MRSA antimicrobial use at our institution along with other safety and clinical [12].

We found a significant difference between the groups for duration of empiric MRSA-targeted therapy. It is important to note that no patients needed MRSA coverage added back due to isolation of MRSA in clinical cultures after initial anti-MRSA therapy discontinuation. This suggests that the use of MRSA nasal PCR as a de-escalation tool not only decreased antibiotic hours, but also did not directly worsen clinical outcomes. Additionally, from a safety standpoint, there was a trend towards decreased rates of AKI in the POST group, which may increase morbidity and cost. There was also a numerical difference in readmission rates with a trend towards higher rates of 9-month readmission due to DFI in the POST group. This could be due to differences in source control in the two arms that was not assessed. In our review of the readmissions in the POST group, all but one of the readmissions did not appear to be related to withholding vancomycin therapy.

Our findings are consistent with published data to support the use of MRSA nasal PCR as a de-escalation tool, which first emerged in patients with pneumonia. Baby and colleagues performed a retrospective analysis of patients who received either vancomycin or linezolid for suspected pneumonia before and after the implementation of a pharmacist-driven protocol for MRSA nasal PCR [9]. They found that the use of MRSA nasal PCR testing in patients with suspected MRSA pneumonia reduced the duration of empiric MRSA-targeted therapy by approximately 2 days without increasing adverse clinical outcomes such as days to clinical improvement, length of hospital stay, or hospital mortality. A growing number of studies have been done to assess utility of MRSA nasal PCR in patients with DFI; however, this is the first study that we know of to report the effect on antimicrobial use in patients with [10–12]. We examined the utility of using an MRSA nasal PCR testing protocol as a de-escalation tool in DFI. Our primary outcome of reduced antibiotic hours aligns well with the previously published study for pneumonia.

Our study has limitations. No blinding was conducted as part of the chart review. The single-center design and veteran population limit generalizability to other populations and institutions. Given the culture specimens are labeled by the surgeons or other providers who obtained them, we are unable to verify whether they are correctly labeled, and not all cultures were obtained surgically. There are significant differences in percentage of MSSA and Gram-negative pathogens isolated in cultures. Our facility did see an increase in prevalence of MSSA between the PRE and POST time periods; however, we are unable to determine a reason for the difference in Gram negatives. We did not assess antibiotics administered in the emergency department or prescribed at discharge, so the reported empiric MRSA-targeted antibiotic therapy use in hours may be underestimated given the duration of treatment for DFI with OM. Additionally, although the aim of this study was not to assess NPV of MRSA nasal PCR, our findings are consistent with other studies in patients with DFI. We did not evaluate patients if they had history of MRSA infection within 1 year prior to the index admission for DFI, which limits our ability to utilize MRSA nasal PCR as a de-escalation tool in this patient population. We also did not collect information on surgical margins given our study includes both DFI with or without OM. We also only treated AKI as a binary variable and did not assess the long-term impact of the therapies on kidney function. Furthermore, we only reported if MRSA coverage was added back for MRSA, which decreases generalizability as vancomycin is not only used for MRSA, but also for beta-lactam resistant organisms, such as Corynebacterium striatum or coagulase negative staphylococci. However, these organisms are often indolent and the risk of waiting for cultures to finalize before initiating therapy is low. We also did not account for variables such as source control, outpatient antibiotic selection, and medication adherence which could have affected hospital readmission rates.

Hospital readmission alone is not the most important or relevant outcome, and it is driven by many factors (e.g., source control, social determinants of health, etc.). Taken together, we believe our secondary outcomes are necessary to get a more complete picture of the patients' experience. Collectively, we believe the chosen primary and secondary outcomes make the case that treatment outcomes of MRSA DFI were similar in the pre- and post-intervention periods.

Though we conducted a sample size calculation for the primary outcome (median hours of inpatient MRSA-targeted antibiotic therapy) before beginning our study, we did not conduct a sample size calculation for the secondary outcomes, including hospital readmission, and it is possible that we did not have enough patients to eliminate the chance of type 2 error for our secondary outcomes. Table 3 depicts the raw numbers for the secondary outcomes involving hospital readmission, but health outcomes such as these are multifactorial, and this study was not designed to collect all the factors that might have had an impact on the secondary outcomes (e.g., source control, social determinants of health, etc.). Furthermore, we did not have 12 months of follow-up for all patients in the post-intervention group. Finally, the VA cost for labs and medications is proprietary, so we cannot determine or report the cost-benefit of the intervention. Nevertheless, we believe this intervention is valuable as an antimicrobial stewardship initiative.

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