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Blood Culture Medium Affects Bacterial Detection, Recovery

The choice of which blood culture medium to use in detecting possible sepsis in trauma and emergency patients can make a difference in time to bacterial detection and recovery, according to an article published in the March 15 issue of Clinical Infectious Diseases.

Rebecca Zadroga, MD, from the Department of Infectious Disease, University of Minnesota, and Hennepin County Medical Center, Minneapolis, and colleagues conducted a head-to-head comparison of 2 widely used blood culture media at a 462-bed acute care trauma center and emergency department between February 1 and September 30, 2011.

They compared the Becton Dickenson Bactec Plus (Bactec) with the bioMériux BacT/Alert FAN (BacT/Alert) in the collection of 9395 cultures. Of those cultures, 831 were included in the analysis, 524 (33%) of which contained pathogens. Exclusion criteria included pediatric patients and a difference in the amount of bottles drawn.

The researchers found that Bactec yielded a 4.5-hour faster bacterial detection time (P < .0001) than BacT/Alert and isolated exclusively 182 (35%) of 582 pathogens (P < .001). They also found that Bactec isolated 136 (39%) of 345 of the gram-positive cocci (P < .001), 48 (27%) of 175 gram-negative rods (P = .02), and 101 (52%) of 195 Staphylococcus aureus (P < .001) and identified 59 (49%) of 120 septic events (P = .004).

"If active antibiotics had been dosed 0–4 or 4–48 hours prior to culture collection, the odds of that culture growing in BACTEC were 4.8- and 5.2-fold greater, respectively, than of growing in BacT/Alert (P < .0001)," the researchers write. "Both were equivalent in the recovery of yeast and when no antimicrobials were dosed."

Time is critical in the diagnosis of sepsis, the researchers write, and guidelines recommend that antimicrobials be initiated within 1 hour of sepsis recognition.

"The reality of this paradoxical relationship between rapid treatment initiation and potential impact on diagnostics is exemplified in our study, as 50% and 82% of patients seen in our wards and [intensive care unit] environments, respectively, had a an antimicrobial administered [prior to culture collection]," the researchers write.

Previous studies have not detected differences among blood culture media in a hospital setting, and it is unclear why this study did show differences, the researchers note. "[D]ifferences in the recovery and [time to detection] for S. aureus is a key finding in our study that has not been previously described," they write.

They conclude, "[T]he diagnosis of sepsis remains both a clinical and laboratory diagnosis."

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