Background: Bloodstream infections are associated with high rates of morbidity and mortality, therefore prompt identification and antimicrobial susceptibility testing of the causative organism(s) are critical. We compared the microbiological/clinical performance of BACT/ALERT®-VIRTUO™-(bioMérieux) to that of the BACTEC™FX-(BD) instrument, with time-to-detection (TTD, from loading into system until positivity) as the primary outcome. Secondary microbiological outcomes were positivity and contamination rates, hands-on-time, turn-around-time (TAT) and time-to-identification.
Materials/methods: We performed a prospective cross-over study using blood cultures from patients (>18 years) suspected of bacteremia/fungemia, localized in different wards into two strata (Stratum-1: Emergency Department-ED-; Stratum-2: in-hospital patients). Testing was performed in BACTEC™-PlusAerobic/F and BACTEC-Lytic/10-Anaerobic/F bottles and incubated in BACTEC™FX, or BACT/ALERT®FA-Plus and FN-Plus bottles and incubated in VIRTUO™. Initially, each strata was randomly assigned to one of the incubators and then alternated every 2-weeks for 6 months (October-16th-2018 to April-16th-2019). All samples were processed in parallel with the same work-flow from the moment they were flagged positive. Maximum incubation time was 5 days.
Results: We included a total of 3898 extractions (7761 bottles) in VIRTUO and 4179 (8306 bottles) in BACTEC. The median age was 69 years for both groups and the samples were equally distributed for each ward (ED: VIRTUO 80.9%, BD 75.1%). The number of blood cultures with at least one positive extraction was 278 (7.1%) for VIRTUO and 193 (4.6%) for BACTEC (p<0.0001). TTD and proportion of aerobic/anaerobic bottles is shown in Table. Hands-on-time was reduced by 15 minutes/day when using VIRTUO.
Conclusions: We have compared in a large scale and in a “real world” setting the performance of two automatic blood culture incubators. TTD differed in both systems depending on the type of bottle (aerobic vs. anaerobic). The number of positive extractions was significantly higher for the VIRTUO incubated samples, which might impact antimicrobial prescription and clinical outcomes.