Background/Case Studies: FDA’s October 2021 requirement for enhanced platelet bacterial detection allows 7-day storage of apheresis split units individually sampled ≥48 hours after collection with 8mL each inoculated into an aerobic (BPA) and anaerobic (BPN) bottle. bioMérieux’s (Durham, NC) BACT/ALERT instruments employ automated colorimetric detection of bacterial CO2 produced by growing microorganisms in leukoreduced (LR) platelet samples. The 3D model requires manual loading/unloading of bottles, occasionally resulting in incubator temperature fluctuations and false alarms. The VIRTUO instrument performs these functions in a closed system. Our large blood center sought to characterize alarms, including false positive (FP) and true positive (TP) bottle rates as we replace 3D instruments with VIRTUOs.
Study
Design/Methods: One 3D and 2 VIRTUO instruments at a single manufacturing/testing site were queried for loaded bottle numbers and alarms when in use from 8/2/21-3/21/23. Alarm investigations require Micro Lab culture of any alarming bottle and all units from the same collection. Negative bottle cultures define a FP, while identical bacteria from the bottle and ≥1 unit define a TP. All alarms from these 3 instruments were investigated per procedures defining culture result interpretation.
Results/Findings: In this period, there were 27,255 BPA & 27,255 BPN bottles loaded onto the 3D and 68,852 each on the VIRTUO. The alarm rate was significantly lower on the VIRTUO with both BPA & BPN bottles versus the 3D (Table). The number of FPs and per-bottle FP rate is also significantly less with the VIRTUO (for all comparisons, p< 0.00001). The TP rate per bottle remains essentially unchanged between platforms (Table). No Cutibacterium acnes was responsible for a TP result during this period, although rates of positives with C. acnes in the BPN bottle and units negative, expired or transfused without incident were significantly higher on the 3D (0.084% vs. 0.044%, p< 0.152). In BPA bottles, FPs comprised 86% of alarms on the 3D, 18.5% on VIRTUO. For BPNs, FP + C. acnes detection was responsible for 90% of 3D alarms and 58% of VIRTUO alarms. Conclusions: With unchanged performance in bacterial detection, but far fewer alarms and FP bottles, the inventory impact is significant, given the loss of all units in a collection (1-4U) awaiting culture results during investigations. The ease of VIRTUO loading/unloading is considered a significant advantage in addition to the dramatic drop in both FP results and workup costs. C. acnes detection in the BPN bottle remains a disadvantage of anaerobic culture, otherwise believed to reduce time to alarms and detect obligate anaerobe contamination.
Importance of research: FP results lead to loss of LR apheresis platelet units screened for bacterial contamination by automated culture. Machine enhancements which limit FPs (with unchanged contamination sensitivity) help maintain the integrity of the platelet supply and improve laboratory efficiency by reducing the number of FP investigations. We demonstrate that a closed robotic system for bottle handling meets these specifications.
