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Journal of Clinical Microbiology, October 2009, p. 3255-3260, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.01045-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Differentiating Culture Samples Representing Coagulase-Negative Staphylococcal Bacteremia from Those Representing Contamination by Use of Time-to-Positivity and Quantitative Blood Culture Methods {triangledown}

Christelle Kassis,1 Gopi Rangaraj,2 Ying Jiang,2 Ray Y. Hachem,2 and Issam Raad2*

The University of Texas Health Science Center at Houston, Division of Infectious Diseases, 6431 Fannin, Houston, Texas 77030,1 The University of Texas M. D. Anderson Cancer Center, Department of Infectious Diseases, Infection Control and Employee Health, 1515 Holcombe Blvd., Houston, Texas 770302

Received 27 May 2009/ Returned for modification 10 July 2009/ Accepted 11 August 2009

Differentiating true coagulase-negative staphylococcal infection from contamination has an important impact on therapeutic implications. Time to positivity reflects bacterial density and may help in the interpretation of blood cultures. We retrospectively reviewed the records of 272 patients from June 2005 to January 2008 for clinical characteristics, microbiological data, and therapeutic outcome. Four groups were identified. The first three groups, as follows, included patients with one positive quantitative blood culture: the low-colony-count group (<10 CFU/ml), the moderate-colony-count group (30 to 100 CFU/ml), and the high-colony-count group (>100 CFU/ml). The control group included patients with two positive quantitative blood cultures and definite coagulase-negative staphylococcal bloodstream infection. The high-colony-count group had shorter time to positivity (≤16 h) than did the low-colony-count group (P < 0.0001). The low-colony-count group had a significantly longer time to positivity, >20 h (P = 0.001), than did the moderate-colony-count group. Even though antibiotics were not provided in 71% of cases and central venous catheter was retained in 83%, the low-colony-count group had a favorable outcome, suggesting that <10 CFU/ml represents contamination. The high-colony-count group, similar to the positive control group, required antibiotics in 81% of cases and central venous catheter removal in 51% (P = 0.001). A time to positivity of ≤16 h reflects high-grade bacteremia with CFU of >100. Similar to the positive control group, these patients required an active therapeutic approach. A time to positivity of >20 h indicates possible contamination with a CFU of <10, and active therapy may not be required.

* Corresponding author. Mailing address: The University of Texas M. D. Anderson Cancer Center, Department of Infectious Diseases, Infection Control and Employee Health, 1515 Holcombe Blvd., Houston, TX 77030. Phone: (713) 792-7943. Fax: (713) 792-8233. E-mail: iraad{at}mdanderson.org

{triangledown} Published ahead of print on 19 August 2009.

Journal of Clinical Microbiology, October 2009, p. 3255-3260, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.01045-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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