Clinical implications of a single <i>Staphylococcus lugdunensis</i> -positive blood culture: true bacteremia vs. contamination

ABSTRACT Staphylococcus lugdunensis is a common skin commensal. However, S. lugdunensis found in multiple blood culture sets is concerning for life-threatening bacteremia. When a single set is positive, the National Healthcare Safety Network classifies S. lugdunensis as a common commensal (contaminant), while multiple publications found bacteremia and suggested an Infectious Diseases (ID) consultation. Here, a retrospective review spanning 9 years at a large health system evaluated the clinical significance of a single-positive S. lugdunensis blood culture when multiple cultures were collected. S. lugdunensis was found in blood cultures from 137 patients, who were stratified into single ( n = 46) and multiple ( n = 91) set-positive groups. The single-positive group was more likely to be deemed contaminants by clinicians, less likely to have a diagnosis of endocarditis or catheter-related bloodstream infection, and less likely to have an intravascular device ( P &lt; 0.01). Treatment occurrence and duration were also statistically different ( P &lt; 0.01). Single-positive cultures were statistically more likely to be polymicrobial ( P = 0.04). Additionally, each case was reclassified as significant bacteremia, indeterminate bacteremia, or contamination using the Souvenir criteria. In single-positive cultures, significant bacteremia occurred less often (12.1% vs. 43.5%, P &lt; 0.01), while contamination was more common (81.3% vs. 32.6%, P &lt; 0.01). Of note, nearly all significant bacteremia cases involved an intravascular device (96.8%). Taken together, these findings suggest single-positive S. lugdunensis blood cultures are often contaminants, but certain clinical features, including intravascular devices, strongly predict bacteremia. IMPORTANCE A single-positive blood culture set with Staphylococcus lugdunensis can be difficult to distinguish between contamination and bacteremia. Conflicting clinical guidance has added to the confusion and emphasizes the need for additional studies. Our results suggest a single-positive S. lugdunensis blood culture set often reflects contamination and polymicrobial cultures, whereas multiple-positive sets strongly predict significant bacteremia. We also identified predictors of significant bacteremia, such as the presence of an intravascular device, emphasizing the need to incorporate additional metrics into clinical decision-making algorithms. Our findings underscore the role of clinical judgment when S. lugdunensis is recovered from a blood culture. Taken together, the proposed practice for the microbiology laboratory is to include a contamination comment on the report of a single-positive S. lugdunensis blood culture set and to recommend an infectious disease consultation for clinical adjudication.