Time-to-detection of bacteria and yeast with the BACTEC FX versus BacT/Alert Virtuo blood culture systems

BACKGROUND: Bloodstream infections are associated with high rates of morbidity and mortality. Rapid detection of bloodstream infections is important in achieving better patient outcomes. OBJECTIVE: Compare the time-to-detection (TTD) of the new BacT/Alert Virtuo and the BACTEC FX automated blood culture systems. DESIGN: Prospective simulated comparison of two instruments using seeded samples. SETTING: Medical microbiology laboratory. METHODS: Blood culture bottles were seeded in triplicate with each of the standard ATCC strains of aerobes, anaerobes and yeast. TTD was calculated as the length of time from the beginning of culture incubation to the detection of bacterial growth. MAIN OUTCOME MEASURES: TTD for the various tested organisms on the two microbial detection systems. RESULTS: The 99 bottles of seeded blood cultures incubated in each of the blood culture systems included 21 anaerobic, 39 aerobic and 39 pediatric bottles. The BacT/Alert Virtuo system exhibited significantly shorter TTD for 72.7 % of the tested organisms compared to BACTEC FX system with a median difference in mean TTD of 2.1 hours (interquartile range: 1.5–3.5 hours). The BACTEC FX system was faster in 15.2% (5/33) of microorganisms, with a median difference in mean TTD of 25.9 hours (IQR: 9.1–29.2 hours). CONCLUSION: TTD was significantly shorter for most of the microorganisms tested on the new BacT/Alert Virtuo system compared to the BACTEC FX system. LIMITATIONS: Use of simulated cultures to assess TTD may not precisely represent clinical blood cultures.