From the Department of Anesthesiology and Intensive Care Medicine and the Center for Sepsis Control and Care (CSCC), Jena University Hospital.
Correspondence to: Frank Bloos, MD, PhD, Department of Anesthesiology and Intensive Care Medicine, Jena University Hospital, Erlanger Allee 101, 07747 Jena, Germany; e-mail: Frank.Bloos@med.uni-jena.de
Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
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We read with great interest the article by Levin et al1 published in an issue of CHEST (March 2013). The authors report that blood cultures obtained via the wire hub of a central venous catheter (CVC) were positive for contaminants four times more often than blood cultures taken from the nonwire hub. It was concluded that the wire might be contaminated due to manipulation in the not completely sterile subcutaneous tissue.
We would like to confirm the report by Levin et al1 with an observation that has confounded a study where we intended to investigate whether cardiopulmonary bypass for coronary artery bypass grafting is associated with a significant bacteremia or DNAemia. We studied 41 patients with on-pump coronary artery bypass grafting and 11 patients with off-pump coronary artery bypass, where we obtained blood cultures and ethylenediaminetetraacetic acid (EDTA) blood after induction of general anesthesia from the wire hub of the freshly inserted CVC. A consecutive blood sample was taken postoperatively immediately after admission to the ICU by sterile venous puncture. Presence of microbial DNA in the EDTA blood was measured by real-time polymerase chain reaction (PCR) with the Light Cycler System 2.0 (Roche Diagnostics) using the SeptiFast multiplex primer set. The patients gave written consent; the study was approved by the local ethics committee.
Before surgery, 34 of the blood cultures taken from the wire hub (61.8%) were positive and mostly revealed skin contaminants (Table 1). Interestingly, only two of the preoperative PCRs concomitantly taken with the blood culture were positive. After admission to the ICU, only one blood culture was positive.
Bacteria identified by blood culture vs DNA amplicons in concomitant EDTA blood samples subjected to PCR. EDTA = ethylenediaminetetraacetic acid; PCR = polymerase chain reaction.
Blood cultures drawn from a CVC are prone to a higher proportion of false-positive results when compared with fresh venipuncture.2 However, such studies addressed CVCs several days after insertion. As in the study by Levin et al,1 we have obtained blood from a CVC just inserted under conditions of maximum barrier precautions. In contrast, the concomitantly obtained PCR did not show such a rate of positivity although they were taken simultaneously with the blood culture. A contamination may remain undetected by the PCR technique because detection cutoff values for coagulase-negative staphylococci and Streptococcus species avoid detection of contaminants.3 In conclusion, this observation confirms the report that blood cultures should not be drawn from the wire hub of an intravascular catheter even if freshly inserted under maximum barrier precaution by the Seldinger technique.
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