Consequences of Implementing a "better" Blood Culture System

Background: Blood cultures (BCx) are the gold standard for diagnosing blood stream infections. However, contamination remains a challenge and can increase cost, hospital days, and unnecessary antibiotic use. National goals are to keep overall BCx contamination rates to ≤3%. Our healthcare system recently moved to a BCx system with better organism recovery, especially for gram-negative, fastidious, and anaerobic bacteria. The study objectives were to determine the benefits/consequences of implementing a more sensitive blood culture system, specifically on contamination rates. Methods: The electronic health record was queried for all BCx obtained within our tertiary-care health system from April 2015 to October 2016. Cultures were divided into those obtained 12 months before and six months after the new system was introduced. A positive BCx was defined as one with any growth. Contaminated BCx were defined as those showing coagulase-negative Staphylococcus, Corynebacterium, Bacillus, Micrococcus, or Propionibacterium acnes. Cultures with Staphylococcus aureus, Klebsiella pneumoniae, or Escherichia coli were said to contain a true pathogen. Results based on hospital location of blood drawing also were determined. Results: A total of 20,978 blood cultures were included, 13,292 before and 7,686 after the new system was introduced. With the new system, positive BCx rates increased from 7.5% to 15.7% (p < 0.001). Contaminants increased from 2.3% to 5.4% (p < 0.001), and pathogens increased from 2.5% to 5.8% (p < 0.001). Contaminated BCx increased significantly in the surgical/trauma intensive care unit (STICU), emergency department (ED), and medical ICU (MICU), while pathogen BCx increased on the surgical floor, ED, and MICU. Conclusions: A new blood culture system resulted in significant increases in the rates of positive, contaminated, and pathogen BCx. After the new system, multiple hospital units had contamination rates >3%. These data suggest that a "better" BCx system may not be superior regarding overall infection rates. More research is needed to determine the impact of identifying more contaminants and pathogens with the new system.