Background: Staphylococcus lugdunensis is a coagulase-negative staphylococcus with similar virulence as S. aureus. Whether S. lugdunensis causes infective endocarditis (IE) in a similar proportion of cases as S. aureus (reported to be 12.6% in a definitive multicenter prospective study) is unclear.
Methods: We conducted a retrospective study of adult patients with at least one blood culture positive for S. lugdunensis at our institution from January 2006 to December 2014. We examined microbiology data, ascertained disease severity and determined the proportion of patients with definite or possible IE based on the 2000 Modified Duke Criteria. Because S. lugdunensis was routinely identified at our institution from 2012 onwards, we determined the proportion of patients with IE before and after implementation of routine speciation. We also compared our results with reported proportions of IE among patients with S. lugdunensis bacteremia (SLB) in other institutions by conducting a systematic review of literature. Nonparametric bootstrapping methods were performed to determine 95% confidence intervals (CI) for proportions of IE in patients with SLB.
Results: 74 patients with SLB were identified, of whom 64% (47/74) had sepsis by SIRS criteria, and 18% (13/74) had severe illness by Pittsburgh bacteremia score (PBS). Kaplan-Meier survival analysis showed that one-year survival among patients with severe illness was worse than patients with non-severe illness (p = 0.02). 15% (11/74) of patients had definite or possible IE (95% CI 6.8 23.0%). The proportion of SLB patients with IE was 15.8% (6/38, 95% CI 5.3 28.9%) prior to routine speciation and 13.9% (5/36, 95% CI 2.8 27.8%) after routine speciation (p = 0.71). Of patients with 2 positive blood cultures or more, 25% (10/40, 95% CI 12.5% - 40.0%) had IE. Systematic review of literature yielded 8 relevant retrospective studies. Of studies that included patients with one or more positive blood cultures for S. lugdunensis, the proportion of IE ranged from 6.3% to 27.0%.
Conclusion: The proportion of IE among patients with SLB is similar to the proportion of IE among patients with S. aureus bacteremia. Our findings suggest that growth of S. lugdunensis in two separate blood cultures should be included as a major criterion in the Duke criteria for IE.
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