Clinical significance of coagulase-negative staphylococci detected in blood cultures

Abstract

There are few reports from Japan on the clinical significance of coagulase-negative staphylococci (CNS) detected in blood cultures, and in many situations, laboratories have difficulty determining the significance of CNS detection. In this study, we investigated the time required to detect blood culture (time to positivity) for CNS, the strains detected, methicillin resistance rate, the presence of a central venous catheter (CVC), positivity from multiple blood culture sets, and the clinical departments among 277 cases with CNS-positive blood cultures. We aimed to determine the criteria with high specificity for clinical significance of CNS detection. Of the 277 cases, 67 cases, 8 and 202 were determined to be clinically significant (25.1%), intermediate (2.9%), and contaminant (73.0%), respectively. The average time to positivity was 19 h and 54 min in clinically significant cases, while it was 31 h and 1 min in contaminant cases, which was significantly longer. Proportions of clinically significant cases by clinical departments were 8.4% for the emergency room and >40% for the departments of gastroenterological surgery, general surgery, hematological oncology, metabolism, and endocrine internal medicine. When CNS was detected in blood cultures, “time to positivity of less than 18 h from cases with CVC” was highly likely to indicate clinical significance, and “time to positivity of longer than 30 h from cases without CVC” was highly likely to indicate a contaminant. Adding these criteria to the first report of positive blood culture will lead to a prompt appropriate antimicrobial therapy when needed, and prevent unnecessary antimicrobial therapy.