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.

Bacteremia in a Veterans Administration Medical Center (1961-1981).

Laboratory data on blood cultures were reviewed for the period 1961-1981. Blood cultures accounted for 18% of all bacterial cultures. Nine percent of all blood cultures were positive for growth, including pathogens and contaminants. Of these, 21% wer contaiminants. Staphylococcus epidermidis was the most common contaminant while Escherichia coli and Staphylococcus aureus were the most frequently occurring pathogens, respectively. Four percent of all positive blood cultures, involving pathogens, had multiple organisms with E. coli the most common. There was no drastic change in the frequency of occurrence of Gram negative or positive isolates over the years, but certain pathogens like Proteus mirabilis, Serratia sp. and Group A Streptococci were more common from 1971-81 than 1961-70. One percent of all patients with positive blood cultures had the same organism for two months or longer. Analysis of these longer occurring infections yielded a mean of 15, median of 7 and range of 2-87 months. E. coli was the most common pathogen in these chronic infections, followed by S. aureus and Streptococcus pneumoniae, respectively.

Seasonal and monthly variation of Streptococcus pneumoniae and other pathogens in bacteremia (1961-1981).

Laboratory data, on positive blood cultures, were reviewed for the period 1961-1981. A total of 1809 episodes of bacteremia and fungemia were evaluated as to monthly occurrence. Of these, 42% were due to Gram positive cocci, 51% to Gram negative bacilli, 5% to anaerobes and 2% to yeasts. When seasonal patterns were categorized, most were bi- or multiphasic except Streptococcus pneumoniae and Staphylococcus aureus which yielded mono- and aphasic patterns, respectively. These results show the occurrence of certain pathogens, like S. pneumoniae, to be linked with seasons or months of the year.