229. Change of Anaerobic Blood Culture Media Increases Isolation of Anaerobic Blood Stream Infections
Session: Poster Abstract Session: Diagnostic Microbiology
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
  • 4 yrs anaerobe IDSA 2013_final.pdf (378.3 kB)
  • Background: Obligate anaerobes are uncommonly isolated from blood cultures, usually comprising from 0.4-4% of overall positive growth, but are associated with mortality rates high as 50%.  Factors influencing obligate anaerobe recovery likely are many, including prior exposure to antimicrobials and the kind of blood culture media utilized. In vitro data has shown that BACTEC Lytic has faster time to detection for anaerobic organisms than does BacT/Alert FN, but whether there is a clinical difference in isolation rates between these 2 is not known. Our hospital changed from BacT/Alert FN medium to BACTEC Lytic anaerobic medium in 2011.  This study identifies differences in isolation rates of obligate anaerobes prior to and after the change of blood culture media. 

    Methods:  All obligate anaerobes isolated for 2 years prior to and 2 years after blood culture media was changed (2/1/2009-2/1/2011 and 2/1/2011-2/1/2013) were evaluated.  Overall culture positivity and obligate anaerobe isolation was tabulated.  Propionibacterium sp. isolates were excluded from the analysis because all isolates were considered contaminants and likely to have overestimated any effect seen.

    Results: A total of 56,404 cultures were collected over the 4 year period.  Overall culture positivity rate in 2009-2010 was 3,184/29,762(10.7%) and 3,146/26,642(11.8%) from 2011-2012(p<0.0001).  The contamination rate was 3.6% for 2009-2010 and 4.0% for 2011-2012.  The number of obligate anaerobes isolated was 58/3,184(1.8%), affecting 53 patients in 2009-2010 and 101/3,146(3.2%), affecting 88 patients  from 2011-2012(p=0.0005).  The most common organisms isolated were Bacteroides sp, Clostridium sp, and Fusobacterium sp with 43, 31, and 9 cases respectively throughout the study period.  There was no statistical difference in specific organism identification between time periods.

    Conclusion:  The overall number of positive cultures and obligate anaerobes isolated increased after the change in blood culture media from BacT/Alert FN to BACTEC Lytic.  Anaerobe isolation nearly doubled (1.8% to 3.2%) but not at the expense of contaminants, as this rate remained flat.  Neither medium has antimicrobial removal components, eliminating this as a possible confounder. It is not known if this difference translates into a difference in mortality or length of hospital stay.

    Rebecca Zadroga, MD1, Richard Gottschall2 and Glen Hansen, PhD2, (1)Infectious Disease, Hennepin County Medical Center, Minneapolis, MN, (2)Microbiology, Hennepin County Medical Center, Minneapolis, MN


    R. Zadroga, None

    R. Gottschall, None

    G. Hansen, Becton Dickinson: Investigator, Research support for project unrelated to presented research

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