Objective: Coagulase negative staphylococci (CoNS) cause health care associated circulatory system infections. They are also the inhabitants of normal skin flora. In this study we aimed to evaluate use of various clinical and laboratory parameters of the patients whose blood cultures revealed growth of CoNS so as to differentiate between infectious agent and contaminant in the blood cultures of these patients.

Material and Methods: The classification of CoNS isolated from the blood cultures as a real pathogen or a contaminant was based on the evaluation of the infection control team that used the CDC criteria. According to this evaluation the study group with CoNS as the infecting agent consisted of 25 patients and the control group with CoNS as the contaminant consisted of 50 patients. The clinical and laboratory parameters were compared using the software of SPSS 21.0. Mann- Whitney U test was used to compare means of the study parameters. Pearson’s khi-square test and Fisher’s exact khi-square test were used to compare the categorical variables.

Results: Two groups were compared in terms of clinical and laboratory parameters. The presence of central venous catheter (p=0.02) and duration of stay in hospital prior to infection (p=0.001) was significantly different between groups. Presence of one or more SIRS criteria (temperature >38°C or <36°C, heart rate >90bpm, leucocyte count >12000 or <4000/mm3, percentage of immature neutrophils >10%) was also compared. There was no difference between two groups in terms of presence of one or more SIRS criteria.

Conclusion: It is hard to differentiate between a pathogen/contaminant CoNS isolated from blood culture set of a patient. The decision becomes even harder if a second blood culture set has not been sent. The laboratory tries to come to a conclusion by considering clinical and laboratory parametres concerning the patient. In our study fever, heart rate, white blood cell count, systolic and diastolic blood pressures, presence of a dialysis catheter, surgery and resistance to methicilline per se did not not help to arrive at a correct conclusion. Differentiation between pathogen and contaminant CoNS grown in blood cultures seems to continue to be one of the most problematic issues in daily practice with respect to both routine microbiology laboratories and clinicians.