A waterfall of susceptibility results: impact of microbiology testing cascade for MDROs

Cascade reporting is an antimicrobial stewardship strategy which selectively reports broad-spectrum antibiotic susceptibility when narrower-spectrum agents are resistant. Three regional laboratories, which provide microbiology services for HCA Healthcare hospitals in Florida, implemented a standardized antibiotic testing cascade for multi-drug resistant organisms. This study evaluated the impact of the testing cascade on time to susceptibility results for carbapenem-resistant Gram-negative organisms. Appropriateness of manual susceptibility test selection was also assessed. Compliance with the testing cascade was 56%. Appropriateness of manual tests in the pre- and post-intervention groups was 87% (257/297) and 96% (310/323), respectively (P < 0.0001). Median time to first manual test result was 23.1 hours (IQR: 19.8-25.2 hours) in the pre-intervention group and 23.9 hours (IQR: 20.2-27.0 hours) in the post-intervention group (P = 0.11). Implementation of a testing cascade did not result in faster manual susceptibility results, however there was a significant increase in testing appropriateness.