Genomic insights into capital-driven transmission and distance-limited outbreaks of CRAB in Zhejiang ICU networks

Abstract Carbapenem-resistant Acinetobacter baumannii (CRAB) is recognized as one of the most common pathogens responsible for nosocomial infections and mortality among patients in intensive care units (ICUs). Currently, the genomic epidemiological characteristics, transmission patterns, and influencing factors of CRAB dissemination within ICUs remain insufficiently investigated. We conducted a multicenter genomic epidemiological analysis of 138 CRAB isolates collected from ICUs of tertiary hospitals across 8 prefecture-level cities in Zhejiang province between 2018 and 2023. Antimicrobial susceptibility testing and whole-genome sequencing were performed on these isolates. By integrating genomic data from the capital city in public database, we identified population structures and reconstructed transmission events to assess dynamic changes over time. Between 2018 and 2023, CRAB isolates from tertiary hospitals in 9 prefecture-level cities in Zhejiang Province predominantly consisted of the Epidemic Super Lineage (ESL) Clade A and B. The profile of antimicrobial resistance genes was strongly associated with phylogenetic lineage. Short-term outbreaks identified using a 5-SNP threshold demonstrated a significant correlation with geographical distances within 178.7 km. Temporal phylogenetic analysis revealed that the prolonged and sustained transmission of CRAB strains across ICUs in Zhejiang originating in the 2010s, showed a temporal association with the expansion of high-speed rail infrastructure in the provincial capital starting in 2010. CRAB in ICUs from 9 hospitals in Zhejiang Province predominantly consisted of the ESL Clade A and B. Geographical distance and transportation are critical factors influencing the transmission of CRAB outbreaks among ICUs in different cities. The provincial capital appears to exert a persistent influence on non-capital cities, which should be interpreted in light of the larger sample size from Hangzhou.