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DOI:
https://doi.org/10.57187/5198

Original article

Vol. 156 No. 7 (2026)

The impact of the revised EUCAST definitions of susceptibility testing categories on the use of antibiotics for Pseudomonas aeruginosa infections: a matched cohort study

Cite this as:
Swiss Med Wkly. 2026;156:5198
Published
29.07.2026

Summary

 STUDY AIMS: In January 2019, the European Committee on Antimicrobial Susceptibility Testing (EUCAST) redefined the categories classifying the clinical effectiveness of antibiotics, changing the meaning of the “I” category from “intermediate” to “susceptible at increased exposure”. We aimed to estimate the effect of this change on the likelihood of carbapenem prescriptions to treat infections caused by wild-type Pseudomonas aeruginosa.

METHODS: We performed a matched cohort study at University Hospital Basel, Switzerland, including patients with urinary or respiratory tract infection caused by wild-type P. aeruginosa. Patients hospitalised between October 2020 and December 2021 (exposure period after implementation of EUCAST criteria) were matched 1:2 by ward and sample type to patients hospitalised between January 2016 and September 2020 (control period). In multivariable conditional logistic regression analysis, we calculated odds ratios (OR) for meropenem use.

RESULTS: During the study period, 32 and 64 patients were included in the exposure and control periods, respectively. After implementation of the new EUCAST criteria, meropenem prescriptions increased from 3.1% (2/64) to 15.6% (5/32). In the multivariable analyses, we observed increased odds for receiving meropenem in the exposure period as first treatment (adjusted OR: 5.22; 95% confidence interval: 0.87–31.41), although not statistically significant, and as first treatment or treatment change (adjusted OR: 11.10; 95% confidence interval: 2.94–41.85).

CONCLUSIONS: At our institution, the implementation of the revised EUCAST criteria was associated with an increased likelihood of meropenem prescription overall for wild-type P. aeruginosa infection. This highlights the need for comprehensive antimicrobial stewardship efforts to promote and ensure adequate implementation of such reclassifications.

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