Genomic epidemiological investigation and effectiveness of multidisciplinary interventions in a multidrug-resistant Acinetobacter baumannii outbreak in a university hospital intensive care unit: A retrospective study

Background A sudden surge in multidrug-resistant Acinetobacter baumannii (MRAB) incidence in a medical–surgical intensive care unit (ICU) in Seoul, Republic of Korea, in December 2023 prompted a molecular epidemiological investigation and multimodal infection control interventions. We aimed to evaluate the effects of these interventions on the outbreak. Methods This study was conducted in a 28-bed mixed medical–surgical ICU. Environmental cultures were collected from 27 high-touch surfaces around MRAB-colonised patients. Whole-genome sequencing (WGS) and single-nucleotide polymorphism (SNP)-based phylogenetic analyses were performed on 14 isolates (10 clinical and 4 environmental) to determine clonality. The multimodal intervention included admission screening, weekly surveillance, pre-emptive contact precautions, increased frequency of cleaning with sodium dichloroisocyanurate, ATP monitoring, and terminal disinfection using aerosolised hydrogen peroxide. The monthly MRAB acquisition rate was analysed using Poisson regression. Results MRAB was isolated from four environmental samples: three ventilator tubes and one blood pressure cuff. SNP-based analysis revealed that 13 isolates belonged to a single outbreak clone (ST195/ST2) with ≤ 7 pairwise single-nucleotide polymorphism (SNP) differences. Notably, the environmental isolate from the blood pressure cuff exhibited no SNP differences from the subsequent clinical isolate, suggesting a direct epidemiological linkage. Post-intervention, the MRAB acquisition rate per 1,000 patient-days decreased significantly, from 18.56 in December 2023 to zero in February 2025 (relative risk, 0.79; 95% confidence interval, 0.722–0.856; p < 0.001). Conclusions WGS identified the nosocomial transmission of MRAB, and multidisciplinary interventions effectively terminated the outbreak. This study highlights the critical role of multidrug-resistant organism screening, isolation, and enhanced environmental management in preventing the transmission of multidrug-resistant organisms in ICUs.