Clinical characteristics and relevance of coagulase-negative Staphylococci other than S. epidermidis by positive blood culture

Abstract

Introduction: Staphylococci is the most commonly isolated bacteria in blood cultures (BC), and is mostly regarded as contamination. However, the clinical relevance and characteristics of CNS other than Staphylococcus epidermidis (Non-SE-CNS) is still unknown. Methods: For the purpose of clarifying the epidemiology and clinical significance of Non-Se-CNS infections, we retrospectively evaluated BC isolates of Non-Se-CNS at our institute from May 2013 to March 2017.Infections were defined as true bacteremia if (1) two or more positive BCs of the same species were present (or detection of the same species in another clinically relevant sample), (2) the patient had clinical symptoms as outlined in the Centers for Disease Control and Prevention's definition of primary blood stream infection8 and the symptoms or markers of inflammation (e.g., fever, symptoms, white cell counts, C-reactive protein, or procalcitonin) were improved after pathogen-directed therapy (e.g. either antibiotic therapy and/or removal of the foreign body in the case of catheter-related blood stream infections suspected) and (3) without any other infection. Results: During the period, 279 patients with BC positive for Non Se–CNS were identified. 44 patients were excluded, either due to missing data or multiple pathogens in the same BC. Among the remaining 235 patients, 67 (29%) were categorized as true bacteremia (n = 43) or possible infections (n = 24). Resistance rate to methicillin among Non-SE-CNS is about 60%, which is lower than those among S. epidermidis of 78%. Conclusion: About 30% of Non-Se-CNS isolates were clinically relevant in our study. Antibiotic susceptibility of Non-SE-CNS is quite different than those of S. epidermidis.

Keywords

• Coagulase-negative staphylococci
• Contamination
• Bacteremia
• Blood culture
• Time to positivity