314 - Changing Coagulase-Negative Staphylococcus Susceptibilities: Can Vancomycin be used less often for treatment?

Poster Number: 314
Publication Number: 314.444

Leya Salis, University of Virginia School of Medicine, Charlottesville, VA, United States; Melinda D. Poulter, University of Virginia, Charlottesville, VA, United States; Nicole Palazzolo, University of Virginia School of Medicine, Crozet, VA, United States; David A. Kaufman, University of Virginia School of Medicine, Charlottesville, VA, United States

Background: Coagulase-negative staphylococcus (CoNS) bloodstream infection (BSI) remains the most common infection treated in the NICU and biggest driver of vancomycin usage. There are few studies of CoNS species susceptibilities and most have demonstrated that ~15% are susceptible to methicillin, providing an opportunity to treat with nafcillin or oxacillin in those cases. If susceptibilities are performed with CoNS infections, this could reduce vancomycin use by 15% reducing the need for levels along with phlebotomy, costs, subsequent dose modification, potential renal effects, and the emergence of antibiotic resistance. This practice will help maintain the efficacy of vancomycin when needed.

Objective: To examine the current susceptibility patterns of CoNS species and effect of reducing vancomycin usage when treating these infections.

Design/Methods: In August 2020, our microbiology laboratory initiated speciation and susceptibility testing for all CoNS BSIs from the NICU. Nucleic acid detection was used to rapidly speciate CoNS organisms and more quickly obtain susceptibility results for the clinical team. If CoNS species were susceptible to oxacillin, the patient was treated with nafcillin instead of vancomycin for the remainder of antimicrobial therapy. Isolates were analyzed for changes in susceptibility over time as well as any differences due to patient factors including gestational age, birthweight, and the presence of a central venous catheter(CVC) at the time blood cultures were obtained.

Results: CoNS susceptibilities were obtained from 62 of 148 (42%) CoNS BSIs over a 4-year time period from 1/1/2018 to 12/31/2021. Speciation and susceptibility testing of CoNS isolates increased from 17% (17 of 98) before to 88% (44 of 50) (p < 0.01) after 8/1/2020. Patient characteristics are summarized in Table 1.  Figure 1 shows the change in susceptibility to oxacillin over time as well as the CoNS susceptibility of other antibiotics such as Clindamycin.  All isolates were susceptible to vancomycin and oxacillin-susceptibility was 12% in the pre-period to 16% in the post period.Conclusion(s): CoNS susceptibility patterns may be changing facilitating the use of nafcillin or oxacillin and reducing vancomycin usage in up to 16% of CoNS BSIs. If feasible and able to be performed promptly, CoNS pathogens should have speciation and susceptibility testing performed. Further study of dosing, safety and efficacy of other antibiotics may further lead to increasing narrower spectrum antibiotic treatment and reducing vancomycin usage for treatment of CoNS infections.
Table 1. Patient Characteristics of Infants with Coagulase-Negative Staphylococcus Bloodstream Infections from 2018 to 2021*Oxacillin-susceptible vs. oxacillin-resistant isolates (P=0.28).
Figure 1. Antibiotic Susceptibility Patterns for CoNS Bloodstream Isolates from 2018-2021.Percentage of isolates susceptible to CoNS for each antibiotic tested plotted in 6-month increments over a 4-year period.