Effect of replacing two non-lytic anaerobic blood culture flasks with one lytic flask on anaerobic bacterial recovery during a concurrent change in blood culture system

INTRODUCTION: Bloodstream infections are a major contributor to global mortality and demand fast and accurate pathogen identification. This study examined the impact of replacing two non-lytic anaerobic flasks with one lytic anaerobic flask on recovery of and time-to-detection (TTD) for anaerobic bacteria.

MATERIALS AND METHODS: We carried out a cohort study including all blood culture flasks from patients aged 18 years and older in the Capital Region of Denmark. In 2018 a blood culture set consisted of two aerobic and two anaerobic flasks. This was changed to two aerobic flasks, one anaerobic lytic flask, and one mycosis flask in 2020. For comparison, we analyzed TTD in the two time periods and examined differences between blood culturing system (BacT/Alert™ vs. BACTEC™).

RESULTS: We included 175,118 unique blood culture sets from 104,519 individual patients. Overall, we observed an increase in the recovery of anaerobic bacteria and a shorter TTD, difference at 100 hours: 0.11% (p < 0.001) in 2020 compared with 2018. These improvements were largely attributable to hospitals that transitioned from the BacT/Alert™ system to the BACTEC™ system (p < 0.001), whereas hospitals already using BACTEC™ in both periods showed only a marginal, non-significant increase in recovery of anaerobic bacteria when analyzed per blood culture set.

CONCLUSIONS: We did not find evidence of reduced sensitivity of detecting anaerobic bacteria by shifting to a single lytic anaerobic flask. These findings support maintaining the current configuration of one lytic anaerobic flask.