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[The number of blood culture bottle sets and the clinical significance of Staphylococcus spp. isolated from the blood culture].

PURPOSE
We investigated the numbers of blood culture and percentage for 2 or more sets in last 3 years, and analyzed the positive blood culture rates based on culture set drawing in 2007. It is considered indispensable to collect two or more sets of blood culture in order to raise positive rates and discrimination ability. However, the papers which studied discrimination ability are rare; we investigated the relation of number of sets and discrimination ability in the case of Staphylococcus spp. isolated from the blood culture bottle.


MATERIALS AND METHODS
In this examination, cases which performed intravascular catheter tip cultivation simultaneously were removed. In Juntendo University Hospital, 124 Staphylococcus spp. isolated from blood culture in 2007 from January to December were examined. All isolates were categorized as true-positives, contaminants, or indeterminate. The categorical decision was made by following factors taken into account: clinical course, physical findings, laboratory data and imaging results. Two or more Infection Control Doctors (ICDs) independently judged the results, and finally, in the weekly ICD round conclusions were determined.


RESULTS
In 2007, 3,674 blood-culture specimens were collected. The objects of isolated bacteria were 14.8% of Staphylococcus aureus, and coagulase-negative staphylococci (CNS) 24.7%. With S. aureus, indeterminate cases decreased from 18.9% for one-set to 4.8% for two-sets (p = 0.24). In the case of CNS, indeterminate cases decreased from 34% for one-set to 7.7% for two-sets (p<0.01).


CONCLUSION
By performing two-set collection, indeterminate cases showed a significant reduction. In particular, S. aureus is a bacterium which often causes blood stream infection. In one-set drawing out, since there are 18.9% of indeterminate cases, there would be a risk of the delay of clinical judgment.