Retrospective Evaluation of Aerobic Blood Culture Contamination Rates in a Tertiary Care Hospital in One Year

Objective: Automated blood culture systems are the most preferred and reliable methods. It is very important and also difficult to distinguish whether the microorganism is causative or a contaminant in blood cultures. The aim of this study is to evaluate blood culture results between January 1, 2012 and January 1, 2013. Materials and Methods: Blood samples were cultured by using the BACTEC 9120 automated system. The decision about the growth being a pathogen or contamination was made through clinical findings, laboratory results, and identification of the same microorganism with the same antibiotic susceptibility patterns from blood samples. Results: Of the blood cultures, 43.8% yielded positive results, and 30.4% of them were identified as pathogens, while 13.4% was evaluated as contaminants. The highest contamination rate of 29.8% was observed in the department of cardiology, and the lowest contamination rate of 1.2% was observed in the department of pediatrics. Methicillin-resistant coagulase-negative staphylococci were the most common organisms (19.4%) isolated from blood cultures and assumed as pathogens. Conclusion: Every laboratory should control contamination rates at least once a year and check the results on whether contamination rates are less than 3% or not. If the rates are more than 3%, necessary measures should be taken. The most important measure is to establish phlebotomy teams or to educate all personnel, if this establishment not possible.