Impact of delayed blood culture bottles incubation on the recovery and detection of microorganisms : Effect of ambient room temperature versus 4°C.

OBJECTIVES

We assessed the impact of holding BC bottles under room temperature (RT) or 4°C for a series of holding times (2 h, 4 h, 8 h, 16 h, 24 h, 48 h, and 72 h) before loading BC into the continuous-monitoring instrument.

METHODS

We used routine patients' BC bottles reported negative at day 5. They were inoculated with a suspension of 50 - 150 CFU (final intended inoculum per bottle) of an overnight culture. Eleven pathogens associated with bloodstream infections were evaluated in this study.

RESULTS

For all the micro-organisms analyzed, the best recovery rate was observed for bottles kept at 4°C, regardless of the holding times. No false-negative (FN) result was identified at 4°C. The time to positivity decreased with an increased preincubation time when the BC bottles were kept at RT. Primarily, a very substantial number of the spiked BC bottles held at RT for more than 24 h failed to be detected as positive by the BD BACTEC™FX.

CONCLUSIONS

Performing a Gram stain and subculture for the BC bottles kept at RT for more than 24 h could avoid the FN results. Even if the best recovery was observed for BC bottles kept at 4°C regardless of their holding times, this still leads to an important delay for the detection and reporting of positive BCs. While this practice should be discouraged, as stated by the current recommendations, BC bottles mistakenly shipped at 4°C could be processed without impacting detection yield. This pragmatic suggestion applied to exceptional pre-analytical situations should be distinguished from the evidence-based recommendations.