Utility of Methicillin-Resistant Staphylococcus aureus Nares Screening for Patients with a Diabetic Foot Infection

Abstract

Treatment of suspected methicillin-resistant Staphylococcus aureus (MRSA) is a cornerstone of severe diabetic foot infections; however, antibiotics can be associated with toxicity. The objective of this study was to determine the negative predictive value (NPV) of MRSA nares screening in the determination of subsequent MRSA in patients with a diabetic foot infection. This was a retrospective cohort study across Veterans Affairs (VA) medical centers from 1 January 2007 to 1 January 2018. Data from patients with an International Classification of Diseases (ICD) code for a diabetic foot infection with MRSA nares screening, and subsequent cultures were evaluated for the presence of MRSA. NPVs were calculated for the entire cohort, as well as for a subgroup representing deep cultures. Additionally, the distribution of all pathogens isolated from diabetic foot infections was determined. A total of 8,163 episodes were included in the analysis for NPV. The NPV of MRSA nares screening for MRSA diabetic foot infection was 89.6%. For the deep cultures, the NPV was 89.2%. The NPV for cultures originating from the foot was 89.7%, and the NPV for those originating from the toe was 89.4%. There were 17,822 pathogens isolated from the diabetic foot cultures. MRSA was isolated in 7.5% of cultures, and methicillin-susceptible S. aureus was isolated in 24.8%. Enterococcus was identified in 14.7% of cultures, Proteus in 7.3%, and Pseudomonas in 6.8% of cultures. Given the high NPVs, the use of MRSA nares screening may be appropriate as a stewardship tool for deescalation and avoidance of empirical anti-MRSA therapy in patients who are not nasal carries of MRSA.

Fear of Missing Organisms (FOMO): the discordance among broad-spectrum empiric antibiotic therapy, microbiologic results, and definitive antibiotic therapy for diabetic foot infections and lower extremity osteomyelitis

“…Hand et al 13 found that the positive and negative predictive values of prior infection or colonization with MRSA for the subsequent recovery of MRSA were 54% and 97%, respectively. Mergenhagen et al 5 evaluated the utility of MRSA nares screening for patients with DFI. The NPV of MRSA nares screening for MRSA DFI was 89.6%.…”

“…1,2 Current guidelines recommend selection of empiric antibiotics based on severity of infection, risk factors for or history of colonization or infection with methicillinresistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, and local prevalence of these organisms. 3,4 Prior studies documented high rates of unnecessary empiric anti-MRSA and anti-pseudomonal therapy 5,6 based on correlation with microbiologic results; however, most of these studies excluded patients with negative or no microbiologic testing. In "real-world" settings, microbiologic testing may not be performed, or testing may be negative due to inadequate sampling, sampling after the initiation of antibiotics, or absence of true infection.…”

Microbiological profile of diabetic foot infections and the detection of mecA gene in predominant Staphylococcus aureus

“…In this study, all 31 coagulase-positive S. aureus were susceptible to novobiocin and all 73 coagulase-negative S. aureus were susceptible to methicillin. An investigation by Mergenhagen et al (35) determined that the prevalence of Staphylococcus aureus isolated from patients with DFUIs was 89.2%, with 7.5% of MRSA and 24.8% of methicillinsusceptible Staphylococcus aureus. Recently, Anafo et al (36) investigated the variety of bacteria in 100 patients with DFUIs in Ghana and found that S. aureus was the most prevalent bacterium showing resistance to penicillin (100%), tetracycline (47.4%), cotrimoxazole (42.1%) and so on.…”

Hidden Fluids in Plain Sight: Identifying Intravenous Medication Classes as Contributors to Intensive Care Unit Fluid Intake

“…A common way to de-escalate empiric broad spectrum antibiotic therapy, especially for respiratory and diabetic foot infections, is through a polymerase chain reaction nares test for methicillin resistant Staphylococcus aureus , which can lead to early discontinuation of vancomycin when negative. 11,12 Another effective de-escalation method is switching from IV to oral administration of antibiotics, when appropriate. Overall, the efforts of antimicrobial stewardship that have been wildly utilized indeed parallel the goals of fluid stewardship.…”