Lemuel R Non1, Carlos A Q Santos2. 1. Division of Infectious Diseases, Washington University School of Medicine, St. Louis, MO, USA. Electronic address: l.non@wustl.edu. 2. Division of Infectious Diseases, Rush University Medical Center, Chicago, IL, USA.
Abstract
BACKGROUND: Staphylococcus lugdunensis is a coagulase-negative staphylococcus with similar virulence characteristics as Staphylococcus 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 cohort 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 coagulase-negative staphylococci were routinely identified to the species level at our institution from 2012 onwards, we determined the proportion of patients with definite or possible 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 the scientific literature. Nonparametric bootstrapping methods were performed to determine 95% confidence intervals (CI) for proportions of IE in patients with SLB. RESULTS: Seventy-four 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). Fifteen percent (11/74) of patients had definite or possible IE (95% CI 6.8-23.0%). The proportion of SLB patients with definite or possible 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). Among patients with at least two positive blood cultures for S. lugdunensis, 25% (10/40, 95% CI 12.5-40.0%) had IE. Systematic review of the literature yielded eight 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 definite or possible IE among patients with SLB is similar to the proportion of IE among patients with S. aureus bacteremia. The proportions of IE among patients with SLB at other institutions fall within the 95% CI yielded by bootstrapping. Our findings suggest that growth of S. lugdunensis in two separate blood cultures should prompt consideration of workup for IE.
BACKGROUND:Staphylococcus lugdunensis is a coagulase-negative staphylococcus with similar virulence characteristics as Staphylococcus 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 cohort 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 coagulase-negative staphylococci were routinely identified to the species level at our institution from 2012 onwards, we determined the proportion of patients with definite or possible 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 the scientific literature. Nonparametric bootstrapping methods were performed to determine 95% confidence intervals (CI) for proportions of IE in patients with SLB. RESULTS: Seventy-four 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). Fifteen percent (11/74) of patients had definite or possible IE (95% CI 6.8-23.0%). The proportion of SLB patients with definite or possible 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). Among patients with at least two positive blood cultures for S. lugdunensis, 25% (10/40, 95% CI 12.5-40.0%) had IE. Systematic review of the literature yielded eight 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 definite or possible IE among patients with SLB is similar to the proportion of IE among patients with S. aureus bacteremia. The proportions of IE among patients with SLB at other institutions fall within the 95% CI yielded by bootstrapping. Our findings suggest that growth of S. lugdunensis in two separate blood cultures should prompt consideration of workup for IE.
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