Clinical Management and Outcomes in Patients with Coagulase-negative Staphylococcus spp. in Lone Blood Culture Sets Benjamin K Battle, Andrew B. Watkins FMOL Health | St. Dominic Background/Purpose: Blood cultures remain the standard for diagnosis of bloodstream infections, but blood culture contamination may lead to inappropriate antimicrobial use and increased risk to patients. Contaminants are often skin flora organisms, and coagulase-negative staphylococci (CoNS) are the most commonly identified microorganisms found in contaminated blood cultures. Differentiating contaminants from true pathogens proves a challenge as these microorganisms could potentially cause true infection. This diagnostic uncertainty and desire to treat may lead to unnecessary or inappropriate antibiotic use and/or Infectious Diseases (ID) consults, which result in clinical and economic burdens for the patient and hospital. St. Dominic Hospital has placed an emphasis on reducing blood culture contamination based on an increase in contamination rates over the last year. This study seeks to characterize the clinical management and outcomes of patients with CoNS growing in lone blood culture sets at St. Dominic Hospital, as well as to analyze overall contamination trends and financial impacts of these potential contamination events. Methodology: This single-center retrospective observational cohort study includes patients admitted to St. Dominic Hospital from January 1, 2025, to August 31, 2025, that are of at least eighteen years of age with CoNS on one set of blood cultures. Patients with blood cultures positive for Staphylococcus lugdunensis or prior blood cultures with CoNS in multiple sets during admission are excluded. The primary objective is to evaluate the use of antibiotics in patients with CoNS in lone blood culture sets. The secondary outcomes include reviewing the overall trend in hospital blood culture contamination rates, frequency of infectious diseases consults, costs attributable to potential contamination events, impact of contamination on pharmacist workload, and outcomes between patients receiving antibiotics for greater than three days compared to those receiving antibiotics for less than three days. Results: A total of 100 patients were included for analysis, with 56 (56%) receiving antibiotics for coagulase-negative Staphylococcispp. in lone blood culture sets, vancomycin serving as the most prevalent antibiotic administered. In the scope of hospital contamination rates, a total of 409 blood cultures in 2025 were characterized as contaminants, accounting for 2.22% of the total blood culture collections. There was no significant difference in mortality regarding patients that received antibiotics for three days or less when compared to patients that received a duration of antibiotics exceeding three days; however, patients receiving a short duration of antibiotics had a significantly shorter length of stay. Infectious disease consults were ordered in 39 patients, with recommendations for ceasing antibiotic use in 19 of the 39 consults. Costs attributable to contamination events were approximately $107,000 per year for the hospital. The increase in pharmacist workload on vancomycin management for patients with potential contaminations neared 18 pharmacist hours per year. Conclusions: Of the patients with CoNS in one of two blood culture sets, vancomycin was the primary agent utilized. The estimated costs attributable to contaminated blood culture sets were primarily driven by laboratory costs. Extended duration of antibiotics did not show improvement in mortality, and shorter treatment durations were associated with overall decreased lengths of stay. Future considerations will be educating on identify potentially contaminated blood cultures, and informing care providers on the outcomes of this study in regards to length of stay and mortality.
