Whole Genome Sequencing reveals two prolonged simultaneous outbreaks involving Pseudomonas aeruginosa high-risk strains ST111 and ST235 with resistance to quaternary ammonium compounds.

Water-bearing systems are known as frequent Pseudomonas aeruginosa (PA) outbreak sources. Still, many older buildings have sanitary facilities in high-risk departments like the ICU. We present two simultaneous prolonged multidrug-resistant (MDR) PA outbreaks detected at the ICU of a pulmonology hospital, which were resolved by whole-genome sequencing (WGS). Outbreak management and investigations were initiated in August 2019 after detecting two patients with nosocomial VIM-2 positive MDR PA. The investigations involved weekly patient screenings for four months and extensive environmental sampling for 15 months. All patient and environmental isolates were collected and analysed by WGS. From April to September 2019, we identified 10 patients with nosocomial MDR PA, including five VIM-2 positive strains. VIM-2-positive strains were also detected in nine sink drains, two toilets, and a cleaning bucket. WGS revealed that of 16 VIM-2-positive isolates, 14 were ST111 that carried qacE, or qacEΔ1 genes, whereas 13 isolates clustered (difference of ≤11 alleles by cgMLST). OXA-2 (two toilets), and OXA-2, OXA-74, PER-1 (two patients, three toilets) qacEΔ1-positive ST235 isolates dominated among VIM-2 negative isolates. The remaining seven PA strains were ST17, ST233, ST273, ST309, and ST446. Outbreak containment was achieved by replacing U-bends, and cleaning buckets, and switching from quaternary ammonium compounds (QUATs) to oxygen-releasing disinfectant products. Comprehension and management of two simultaneous MDR PA outbreaks involving the high-risk strains ST111 and ST235 were facilitated by precise control due to identification of different outbreak sources per strain, and by the in silico detection of high-level QUATs resistance in all isolates.

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