Successful implementation of a bundle to prevent increased excessive-spectrum antimicrobial use under new EUCAST susceptibility definitions: a quasi-experimental study in a tertiary hospital.

BACKGROUND

This study evaluated the effectiveness of an implementation-bundle to prevent increased targeted excessive-spectrum antibiotics for wild-type Pseudomonas aeruginosa (PA) infections, following the introduction of 2019 EUCAST susceptibility categories redefinition.

METHODS

This was a single-centre, quasi-experimental study at a tertiary University Hospital. All consecutive adult patients with wild-type PA infections between July 2023 and April 2024 were included and analysed across three-month periods: before the EUCAST update (Period 1), after the update with audit-feedback (Period 2), and after the update without audit-feedback (Period 3). The implementation-bundle included: (1) in-person educational sessions before the introduction of the redefinition; and (2) in antimicrobial susceptibility reports, replacing 'I' with 'SE', with a clarifying footnote and dosing information. An audit-feedback intervention was conducted during the first three months after the introduction of the redefinition. Selective reporting of antimicrobial susceptibility testing results was already in place in our hospital. Primary outcomes included targeted meropenem, and ceftolozane/tazobactam prescriptions; secondary outcomes were optimal anti-pseudomonal dosing and infectious diseases (IDs) consultations.

FINDINGS: Among 158 patients (55 Period 1, 60 Period 2, 43 Period 3), targeted meropenem prescriptions did not increase (7.3% vs 6.7% (P=0.898) vs 0% (P=0.071)). No patients received targeted ceftolozane/tazobactam. ID consultations decreased (56.4% vs 38.3% (P=0.053) vs 34.9% (P=0.034)) and correct anti-pseudomonal dosing improved (70.9% vs 93.3% (P=0.002) vs 95.3% (P=0.002)). Risk factors for targeted meropenem prescriptions included age <65 years, immunosuppression, septic shock, intensive care unit admission, and empirical excessive-spectrum antimicrobial use.

CONCLUSION

This implementation-bundle enabled the introduction of EUCAST susceptibility categories redefinition without increasing targeted excessive-spectrum antibiotics or ID consultations, while optimizing dosing.