Impact of intensive care unit relocation on the transmission dynamics of carbapenem-resistant Acinetobacter baumannii: a genetic epidemiology study

Introduction Intensive care unit (ICU) relocation provides a unique opportunity to assess the impact of environmental renewal on the transmission of multidrug-resistant organisms (MDROs). This study aimed to utilize whole-genome sequencing (WGS) combined with epidemiological data to trace changes in the infection rate and transmission routes of carbapenem-resistant Acinetobacter baumannii (CR Ab ) during ICU relocation, and to evaluate the concurrent implementation of infection control measures. Methods Clinical and environmental samples were prospectively collected from a tertiary care hospital in China across three phases: pre-relocation, post-relocation, and post-intervention. Antibiotic susceptibility testing of CR Ab isolates was performed using the Kirby-Bauer disk diffusion method and the VITEK-2 system. WGS was performed on all isolates. A phylogenetic tree was constructed based on core-genome single nucleotide polymorphisms (SNPs), and potential transmission chains were inferred. Infection prevention and control indicators for MDROs were also monitored. Results A total of 11 CR Ab isolates were collected, comprising 10 from patient clinical samples and one from the surface of a disinfected mattress. All isolates demonstrated highly similar antimicrobial resistance profiles and carried a core set of resistance genes, including bla OXA-23, bla OXA-66, bla ADC-73, ant (3'')-IIa, adeB , adeG , and adeJ , with some also harboring bla TEM-1. All CR Ab isolates as sequence type 2 (ST2). Core-genome SNP phylogenetic analysis clustered the 11 isolates into two clades: Clade 1 contained three isolates, and Clade 2 contained eight isolates. This clustering was consistent with the distribution of resistance genes, and two possible transmission chains were constructed. Over the three-month period surrounding the ICU relocation, the CR Ab infection rate exhibited a decreasing trend, hand hygiene compliance improved gradually, and adherence to MDRO isolation protocols increased significantly following interventions by the infection control department ( P < 0.05). Conclusions Although ICU relocation contributed to a reduction in CR Ab infection rates through environmental renewal, it did not completely interrupt transmission. WGS analysis integrated with epidemiological data suggested that environmental contamination and patient carriage likely played critical roles in CR Ab transmission. Enhanced environmental cleaning and disinfection, improved hand hygiene compliance, and strict isolation of infected patients are crucial for the effective control of MDRO spread.