Discrepancies Between Microbial Detection and Identification using the Blood Culture Identification (BCID) FilmArray Panel Assay and Standard Subculture of Positive Blood Culture Bottles

Background:

The BCID panel is a multiplex PCR assay which detects multiple bacteria and yeast as well as select antimicrobial resistance genes, directly from positive blood culture bottles. We currently use this test primarily for work-up of Gram-positive cocci and yeast in blood culture bottles; we have noted occasional discrepancies with results of conventional testing.

Methods:

We reviewed discrepancies between the BCID panel and standard blood culture bottle subculture results vis-à-vis microbial identification in our routine clinical practice.

Results:

A total of 1,496 BCID test results were reported from January 2015 to March 2016. There were 26 apparent discrepant detections, including Candida parapsilosis (n=12), Candida krusei (n=2), Candida tropicalis (n=1), Candida glabrata (n=1), Proteus species (n=7), Enterococcus species (n=2) and Staphylococcus species (n=1). In ten of the C. parapsilosis cases, two C. krusei cases, and the single C. tropicalis case, no yeast were seen on Gram stain or isolated in culture. In the other two C. parapsilosis cases, yeast were seen on Gram stain, but only C. glabrata (co-detected by the BCID panel) was detected in culture. In the C. glabrata case, no yeast were seen on Gram stain or isolated from that blood culture bottle, but C. glabrata was recovered from another bottle from the same patient. In the seven cases of Proteus detection, Gram strain showed only Gram-positive cocci and no Proteus species were recovered in culture. In nine of the C. parapsilosis cases, one C. krusei case and the single C. tropicalis case, there was no clinical evidence of systemic candidiasis and the patients had good clinical outcomes with no antifungal therapy. In one C. parapsilosis case, the patient received caspofungin for C. glabrata fungemia and had a good clinical outcome. In two C. parapsilosis cases, the patients died of unrelated causes. Finally, in one C. krusei case, the patient received fluconazole as prophylaxis for neutropenia and remained clinically stable.

Conclusion:

In routine use in our clinical practice, the FilmArray BCID panel detects organisms neither seen on Gram stain nor recovered in culture in 1.7% of cases, with C. parapsilosis and Proteusspecies being the most commonly involved organisms.