Recovery of clinically important microorganisms from the BacT/Alert blood culture system does not require testing for seven days.

Recently, we published a comparison of the BacT/Alert blood culture system with the BACTEC 660/730 nonradiometric blood culture system using blood inocula of 5 ml per bottle. By reanalyzing data collected during that study, we found that, for true-positive isolates causing bacteremia or fungemia, 363 (97.6%) of 376 and 341 (97.7%) of 349 isolates were recovered by the end of day 5 of testing, and 364 (97.9%) of 376 and 343 (98.3%) of 349 isolates were recovered by the end of day 6 of testing for aerobic and anaerobic bottles, respectively. Most isolates recovered on days 6 (24 of 27) and 7 (20 of 25) of testing were either contaminants or indeterminate as a cause of sepsis. When used as recommended by the manufacturer, only six (1.3%) of 464 clinically important isolates recovered on test days 6-7 would have gone undetected had testing been limited to 5 days and four (0.9%) of 464 had testing been limited to 6 days. We conclude that BacT/Alert bottles can be tested for as few as 5 days and then discarded with minimal loss of true-positive isolates and maximal reduction of contaminants.