Impact of CLSI and EUCAST breakpoint discrepancies on reporting of antimicrobial susceptibility and AMR surveillance

We investigated the impact of breakpoint discrepancies between CLSI and EUCAST on susceptibility interpretation of clinical isolates at the Microbiology Laboratory, Mahosot Hospital, Vientiane, Laos and performed a literature search to compare our findings to published reports. Zone diameters for first-line antimicrobial agents tested against non-duplicate clinical isolates of Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa in 2017 were interpreted separately using EUCAST 2018 and CLSI 2018 breakpoints and greement measured. Applying EUCAST instead of CLSI breakpoints to 428 E. coli, 208 K. pneumoniae and 78 P. aeruginosa isolates would have increased rates of ciprofloxacin resistance (59.1% vs 46.5% in E. coli, 37.5% vs 13.9% in K. pneumoniae, 28.2% vs 10.3% in P. aeruginosa) and amoxicillinclavulanic acid resistance (52.3% vs 19.9% in E. coli, 35.6% vs 22.1% in K. pneumoniae). Our results are supported by a literature search which identified 20 articles whose main objective was comparing susceptibility interpretation between CLSI and EUCAST. 19/20 articles reported significant discrepancies in one or more pathogen-antimicrobial combinations, nearly always due to a reduction in susceptibility rates and/or increase in resistance rates when applying more restrictive EUCAST breakpoints. We conclude that breakpoint discrepancies between CLSI and EUCAST have a significant impact on susceptibility interpretation of clinical isolates and AMR surveillance initiatives, and highlight the need for globally harmonized clinical breakpoints