A comparison of pathogens and contaminants based on the number of positive blood cultures in a set.

A total of 2766 positive blood cultures, from the Veterans Administration Medical Center in Oklahoma City (1961-1981) were evaluated to determine the relationship of organism, pathogenicity and number of cultures (blood culture bottles) positive. Most patients had 2-4 blood cultures drawn. Organisms which are usually considered as nonpathogenic (Bacillus, Propionibacterium) were mostly found in only one of the cultures. Whereas those microorganisms which are considered pathogenic were most often found in two or more cultures. Organisms like Staphylococcus epidermidis are the most difficult to classify because they can be either pathogenic or contaminant. If an organisms which is normally considered a nonpathogen is found in two or more cultures, it should be considered as a potential pathogen until proven otherwise.