The effectiveness of the skin antiseptic may be an important factor in determining contamination rate in blood culturing. If these results are confirmed by others, then institutions that have a high blood culture contamination rate when using an iodophor for skin preparation should consider changing to iodine tincture.
This is a study of 130 matched venipuncture and intravascular blood cultures collected from 53 patients. In 99 cultures (76.1%), both the venipuncture and the catheter specimens were negative. There were six matched cultures yielding significant isolates: in three both the venipuncture and intravascular specimens were positive; in two only the intravascular specimen was positive; and in one only the venipuncture specimen was positive. Twenty-five cultures were positive from the intravascular specimen only, and 23 of these were classified as contaminated cultures. Thus, the contamination rate was significantly higher in the intravascular catheter blood culture specimens (P less than 0.001). These results indicate that blood culture specimens should not be routinely collected from intravascular catheters unless collection by venipuncture is impossible.
For patients with suspected bacteremia, at least two separate blood cultures are recommended to achieve maximum sensitivity and to properly interpret results. Since a single blood collection may signify an improper procedure with serious consequences if the diagnosis of blood stream infection is missed, we investigated this problem with studies at three teaching hospitals (A, B, and C) and by a survey of 38 other hospitals. The incidence of solitary blood cultures ranged from 1 to 99% (median 26%) at the surveyed institutions. Among the cases investigated at hospitals B and C, between 10 and 30% of solitary blood cultures were not clinically indicated, while most of the others were caused by the physician not knowing that one culture was insufficient or by failure to complete the diagnostic plan. Focused concurrent intervention at hospital B was associated with reductions in solitary blood cultures from 40.0 to 24.6% (p = 0.045) and a decline in those not indicated from 38.1 to 12.5% (p = 0.192). Global educational efforts at hospital A were associated with a decrease in solitary blood culture rates from 52 to 37% (p = 0.016). These results show that blood culture practice varies widely among institutions in spite of consensus recommendations for proper specimen collections. We estimate that, nationwide, up to 18,000 etiologic diagnoses of bacteremia are missed annually because of this problem. Monitoring institutional solitary blood cultures is recommended as a test utilization indicator and as the basis for improving blood culture practice.
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