Quantitative blood cultures - Their value with laboratory contaminants

A total of 142 patient records were evaluated to determine if the isolation of Staphylococcus epidermidis, Propionibacterium acnes or diphtheroids were associated with clinical signs of septicemia. Where possible, an attempt was made to correlate cfu/ml of patient blood and time to positive isolate with clinical significance. With positive cultures for Staphylococcus epidermidis, the following was observed: With a blood count of <1 cfu/ml no clinical signs of septicemia could be documented. In the two cases of confirmed septicemia, the initial cfu/ml was ≥ 6.9 cfu/ml. Based on time to positive, it may prove feasible to separate septicemia and skin contamination (positive within 2 days) from laboratory contamination (positive from day 1 through day 6). Of 15 patients with diphtheroids, the cfu/ml was always < 1 /ml and no clinical signs of septicemia by this organism were noted. Finally, in 10 patients with Propionibacterium acnes bacterial counts ranged from a low of 0.1 to a high of 17.2 cfu/ml and no isolate was recovered until day 4 or later. No documented septicemia was observed. This study suggests that bacterial counts of <1 cfu/ml for common contaminants are not indicative of septicemia and that the time to positive isolate may prove useful in distinguishing between skin and laboratory contamination.