CONTROLLED EVALUATION OF 5-MILLILITERS VERSUS 10-MILLILITERS OF BLOODCULTURED IN AEROBIC BACT ALERT BLOOD CULTURE BOTTLES/

Bottles developed for use in the BacT/Alert automated blood culture sy stem (Organon Teknika Corp., Durham, N.C.) can accept up to 10 ml of b lood without falling below a 1:5 ratio of blood to broth. We compared the yield and speed of detection of microorganisms in 13,128 adequatel y filled, paired, aerobic bottles inoculated with 5 versus 10 ml of bl ood at three university hospitals. A total of 798 microorganisms causi ng sepsis grew in one or both bottles. The overall recovery of microor ganisms from 10-ml samples exceeded that from 5-ml samples (P < 0.001) ; the increased yield attributed to the additional 5 ml in the samples was 7.2%. The increased yield from 10-ml inocula was most marked for Escherichia coli (P < 0.01) and other members of the family Enterobact eriaceae (P < 0.001). Ten-milliliter samples did not yield more gram-p ositive bacteria, nonfermentative gram-negative rods, or yeasts. When both bottles were positive, the bottles inoculated with 10 ml of blood showed growth sooner (P < 0.001). Earlier detection with 10-ml inocul a was especially notable for coagulase-negative staphylococci (P < 0.0 01), streptococci (P < 0.001), E. coli (P < 0.025), and other members of the family Enterobacteriaceae (P < 0.025). We conclude that an incr ease in the volume of blood inoculated into BacT/Alert aerobic blood c ulture bottles from 5 to 10 ml will increase the overall yield and the speed of detection of clinically important blood pathogens.