From high-touch surfaces to air: A prospective genomic analysis unveils an underestimated transmission route of carbapenem-resistant Acinetobacter baumannii in the ICU

OBJECTIVES: To investigate the extent of environmental contamination around carbapenem-resistant Acinetobacter baumannii (CRAB)-positive patients and to explore the role of environmental factors in the pathogen's transmission dynamics. METHODS: Prospectively collected CRAB-positive specimens from intensive care unit (ICU) patients and their immediate environments from September 2024 to April 2025. Positive detection rates were quantified and statistical analyzed by sample type, and whole-genome sequencing (WGS) was employed to determine phylogenetic relationships and evolutionary dynamics among the isolates. RESULT: The overall environmental positivity rate in patient bed units was 13.08%, significantly higher than in other public areas (P < 0.001). High-touch surfaces (HTS) and air sampling sites samples showed markedly higher positivity rates compared to healthcare worker-related sites (HWS) samples (P < 0.001). HTS sample with direct patient or body fluid contact exhibited higher bacterial loads (HR = 1.623, 95% CI 1.178-2.237, P = 0.03), and HWS samples yielded similar findings (HR = 2.325, 95% CI 1.167-4.632, P = 0.016) for HWS), while air samples demonstrated distinct growth kinetics. WGS analysis identified ST2 as the predominant strain, while airborne isolates displayed greater genetic diversity than HTS isolates (P = 0.013), and we successfully reconstructed two potential transmission events. CONCLUSION: The airborne transmission route of CRAB has been substantially underestimated, necessitating the urgent implementation of additional infection control measures to limit its spread within ICUs.