Five-year VIM-producing Pseudomonas aeruginosa outbreak in four Belgian ICUs, an investigation report (2019-2023)

Background: Verona integron-encoded metallo-β-lactamase-producing Pseudomonas aeruginosa (VIM-PA) outbreaks are frequently linked to contaminated sink-drains in the intensive care unit (ICU). This study aims to investigate a VIM-PA outbreak occurring at 4 ICUs in a Belgian university center. Methods: Between 01/01/2019 and 30/07/2023, data were retrospectively retrieved. Whole-genome sequencing of VIM-PA was carried out for available isolates and the core genome multilocus sequencing typing (cgMLST) was used to confirm clonality. New case incidence was estimated by analyzing the weekly data of at-risk and VIM-PA-colonized patients, fitting a regression model. Results: Fifty-one patients were colonized, among them, 32 (63%) were infected by VIM-PA, which contributed to 7 deaths. The outbreak investigation showed that 19 (47%) of the examined sink-drains grew at least once a VIM-PA. Two major clusters were observed by cgMLST: ST111 (59 clones with 40 clinical isolates), and ST17 (8 clones with 6 clinical isolates). The estimated incidence rate of new cases was significantly higher in one unit. Conclusions: A 5-year prolonged outbreak at the UZ Brussel ICUs was caused by only 2 VIM-PA clones, both linked to sink-drains, with minimal mutations occurring throughout the years. Statistical modeling found different incidence rates between units. Tailored interventions were hence prioritized.