Impact of the 2020 EUCAST ‘I’ definition on the treatment of Pseudomonas aeruginosa infections: A national multicentric observational study in Belgian hospitals. 33rd International Congress of Antimicrobia

Impact of the 2020 EUCAST « I » definition on the treatment of Pseudomonas aeruginosa infections: a national multicentric observational study inBelgian hospitals
Laura Bonacini¹, Boudewijn Catry^1,2, Lucy Catteau^1,3
1 Department of Epidemiology and public health, Sciensano, Brussels, Belgium.
2 Faculty of Medicine, Université libre de Bruxelles, Bruxelles, Belgium.
3 Department of Epidemiology and public health, Sciensano, Brussels, Belgium, Faculty of Medicine and Pharmacy, Université de Mons, Mons, Belgium.

AIM: To examine the impact of revisions by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) on antibiotic selection for treating Pseudomonas aeruginosan infections in Belgian hospitals.

BACKGROUND: In 2020, EUCAST redefined the 'I' category in antimicrobial susceptibility testing to 'susceptible, increased exposure,' aiming to optimize antibiotic therapy byadvocating targeted narrow-spectrum antibiotics at higher doses, rather than broader spectrum antibiotics at standard doses. By July 2022, Belgian labs were encouraged to adopt thesechanges, categorizing most antipseudomonal drugs as 'I' while retaining broad-spectrum antibiotics as 'S'.

METHODS: Between November 2023 and May 2024, all Belgian hospitals were invited to participate in a voluntary multicentric retrospective observational study. Data were collectedusing a Redcap tool, focusing on hospitalized adults treated for wild-type
Pseudomonas aeruginosa infections during a six-month period pre- and post-implementation of the newEUCAST definitions. Collected data included epidemiological, microbiological, clinical, and antimicrobial therapy details. The primary outcome assessed was the frequency ofmeropenem prescriptions following susceptibility testing.

RESULTS: The study included 1705 patients (850 pre- and 855 post-implementation) from 38 hospitals (37% nationwide participation). Meropenem prescription significantly increasedpost-EUCAST update, rising from 4.6% (39/850) pre-implementation to 7.1% (61/855) post-implementation. This increase was observed in 47% (18/38) of the participating hospitals.

CONCLUSIONS: The 2020 EUCAST criteria implementation led to a significant increase in meropenem prescriptions for P. aeruginosa infections. This underscores the need for furtherresearch into prescribing practices and reinforces the importance of prescriber education and antibiotic stewardship programs.