Comparison of BACTEC 9240 and BacT/Alert blood culture systems in an adult hospital

In a study comparing the BACTEC 9240 (Becton Dickinson, Canada Inc., Mississauga, Ontario, Canada) and the BacT/Alert (Organon Teknika, Scarborough, Ontario, Canada) blood culture systems, 6,437 sets of four bottles of 10,412 cultures submitted were deemed acceptable for evaluation. There were 586 clinically significant isolates from 544 positive blood cultures. Of the 544 positive blood cultures, 329 were positive in both systems, 157 were positive in the BACTEC 9240 system alone, and 58 were positive in the BacT/Alert system alone (P < 0.001). These cultures represented 421 bacteremic episodes, of which 290 were detected by both systems, 84 were detected by the BACTEC 9240 system alone, and 47 were detected by the BacT/Alert system alone (P < 0.001). The difference between the two systems in terms of microbial recovery was attributable largely to differences in the ability to grow staphylococci. Of 82 monomicrobial isolates of Staphylococcus aureus, 46 were isolated by both systems, 30 were isolated by the BACTEC 9240 system alone, and 6 were isolated by the BacT/Alert system alone (P < 0.0001). A similar pattern was noted in the case of coagulase-negative staphylococci, of which 48 were isolated in both systems, 46 were isolated in the BACTEC 9240 system alone, and 5 were isolated in the BacT/Alert system alone (P < 0.0001). The false-positive rate in the BACTEC 9240 system was 0.5%, and that in the BacT/Alert system was 1.2%. Both systems provided satisfactory service mechanically, and in terms of computer software and costs, both systems were similar. The differences in the recovery of organisms, notably staphylococci, may be due in part to the fact that in the present study the BacT/Alert medium did not contain antimicrobial agent-removing devices, whereas the BACTEC 9240 medium did. Until this difference is resolved, we consider the BACTEC 9240 system to more adequately meet our hospital's requirements.