Blood culture time to positivity

August 25, 2008

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Time to blood culture positivity can assist in excluding a catheter-related blood stream infection as the source an infective episode. This article by Ben-Ami et al (2008) examines this issue in relation to Candidemia.

Ben-Ami, R., Weinberger, M., Orni-Wasserlauff, R., Schwartz, D., Itzhaki, A., Lazarovitch. T., Bash, E., Aharoni, Y., Moroz, I. and Giladi, M. (2008) Time to blood culture positivity as a marker for catheter-related candidemia. Journal of Clinical Microbiology. 46(7), p.2222-6.

Abstract: Candida spp. are important causes of nosocomial bloodstream infections. Around 80% of patients with candidemia have an indwelling central venous catheter (CVC). Determining whether the CVC is the source of candidemia has implications for patient management. We assessed whether the time to detection of Candida species in peripheral blood (time to positivity [TTP]) can serve as a marker for catheter-related candidemia. Prospective surveillance of Candida bloodstream infection was conducted in two medical centers. TTP was recorded by the BacT/Alert automated system. Sixty-four candidemia episodes were included. Fifty patients (78%) had an indwelling CVC. Thirteen patients (20.3%) had definite catheter-related candidemia. TTP was shorter for definite catheter-related candidemia (17.3 ± 2 h) than that for candidemia from other sources (38.2 ± 3 h; P < 0.001). A TTP cutoff of 30 h was 100% sensitive and 51.4% specific for catheter-related candidemia (area under the receiver-operator characteristic curve of 0.76). We conclude that TTP in peripheral blood is a sensitive but nonspecific marker for catheter-related candidemia and that a TTP of more than 30 h can help exclude an intravascular catheter as the possible source of candidemia.