Clinical significance of coagulase-negative Staphylococci isolated from blood cultures

Abstract

Objective To analyze clinical characteristics of bloodstream infections caused by coagulase-negative Staphylococci (CNS) and antibiotic resistance of the bacteria, so that to provide basis for the clinical diagnosis and treatment. Methods A retrospective analysis of CNS in blood cultures collected from 108 hospitalized patients in Puai Hospital of Tongji Medical College from January 2016 to December 2017 was performed. The antimicrobial susceptibilities were tested by Kirby-Bauer method and E test method. For measurement variables, normally distributed variables were compared using t test, and non-normal distributed data were compared using Mann-Whitney U test. Categorical variables were compared using χ2 test. Results Of the 108 patients, 66 were male and 42 were female; the age range was 26 to 98 years and the average was 49 years. According to the criteria for bacteremia, 36 of 108 (33.3%) patients with CNS-positive blood cultures were diagnosed with bacteremia and 72 (66.7%) cases were contaminated. CNS bacteremia mainly occurred in the intensive care unit and nephropathy ward. Among them, 23 (62.2%) patients were catheter-related blood stream infections, and 11 (29.7%) patients were dialysis catheter-related bloodstream infections. Fifteen of 36 (41.7%) strains were isolated within 48 hours of admission. The level of serum procalcitonin (PCT) for bacteremia patients was 2.56 (1.44, 7.60) μg/L, and that was 0.13 (0.05, 0.23) μg/L in contaminated patients. The difference was statistically significant (Z=8.097, P 0.05). After antibiotic treatment, 26 of 36 bacteremia patients were survived. The PCT levels before antibiotic treatment were 2.05 (1.42, 4.32) μg/L, and 0.24 (0.07, 0.61) μg/L after antibiotic treatment. Serum PCT was decreased significantly after antibiotic treatment (Z=4.457, P 0.05). No significant difference was found in white blood cell count between survivors and deaths at 28 days (t=0.771, P>0.05). There was no statistical difference of the anti-bacterial drug susceptibility between pathogens and contaminants (P>0.05). All strains were sensitive to vancomycin, teicoplanin and linezolid. Conclusions The incidence of CNS contamination in blood culture is relatively high. It is important to distinguish true bacteraemia from contamination by a review of the clinical and laboratory indicators. PCT is of clinical value to indicate CNS infection and to monitor therapeutic effect. Key words: Bacteremia; Coagulase negative Staphylococci; Procalcitonin