How to Determine a Contaminant vs True Infection 



What is the organism? Most 

common contaminants: 

 • Coagulase-negative Staph (82%) 

 • Corynebacterium (not jeikieum) (>88%) 

 • Bacillus spp. (not anthracis) (>92%) 

 • Propionibacterium acnes (>94%) 

 • Viridans group streptococci (50-55%) 



How many blood culture sets are 

positive? 

• More likely real if 2 out of 2 sets 

• Caveat: 2/2 is common for coag-neg Staph. Can check antibiograms (100% sensitive for same strain, 84% specific) or get species from the micro lab 



Original Slide by Dr. Jennifer Babik



#BloodCultures #Contaminant #Contamination #Diagnosis #BCx #Laboratory #Interpretation