Retrospective Analysis of the Clinical Significance of Positive Blood Cultures in the Emergency Department: A Single-Center Study

Background There have been major advances in blood culture technology in the last decade, with both faster and more sensitive pathogen detection as well as more precise species identification. We have reassessed the results of positive blood cultures in this new clinical microbiology era with a focus on contaminant identification.Methods A retrospective study was conducted including all patients with a blood culture collected in 2 UMass Memorial Health emergency departments from September 2019 through April 2020. Contaminants were identified based on standard clinical microbiology laboratory criteria and independent retrospective review by 3 infectious disease (ID) physicians and an ID fellow.Results Of 5673 blood samples obtained, 5661 were analyzed after 12 were deemed inconclusive by the ID physician review. Blood culture contaminants accounted for 22.5% of the positive blood cultures. Staphylococcus epidermidis was the most frequent contaminant (33.4%), while Escherichia coli was the most frequent pathogen (21%) causing true bacteremia. Coagulase-negative staphylococci remain the most frequent cause of blood culture contamination with S epidermidis being the most common. The Staphylococcus species S auricularis, S caprae, S lentus, S pseudointermedius, S saccharolyticus, and S warneri were all determined to be contaminants in 100% of cases.Conclusions The improvements in clinical laboratory technology enable better discrimination of the relative pathogenicity of differing coagulase-negative staphylococci species.