# Investigation and control of a suspected outbreak of carbapenem-resistant Acinetobacter baumannii nosocomial infections in the cardiovascular surgical ICU based on whole-genome sequencing

## TL;DR

This study investigated a suspected outbreak of CRAB infections in a hospital ICU using genome sequencing to trace transmission and improve infection control.

## Contribution

The study used whole-genome sequencing to identify potential transmission routes and risk points in a CRAB infection cluster.

## Key findings

- CRAB infections were not part of a single outbreak but showed clonal transmission patterns.
- The urine bag drainage valve switch was identified as a potential transmission risk.
- Environmental and patient strains showed close phylogenetic relationships, suggesting local spread.

## Abstract

The treatment of carbapenem-resistant Acinetobacter baumannii (CRAB) infection faces great challenges. The purpose of this study was to investigate a suspected outbreak of CRAB infections in a cardiovascular surgical ICU to provide reference for clinical prevention and control.

Patients infected with CRAB from 4 August to 29 August 2023 were included. Epidemiological investigation, environmental hygiene testing and pathogen testing were carried out. The whole genome sequencing and homology analysis were conducted to find out the possible infection source and transmission route, and corresponding control measures were taken in time.

Six patients developed CRAB lower respiratory tract infection in the short term, and five of them had similar drug sensitivity results. A total of 21 CRAB were detected from 146 environmental surfaces and the hands of medical staff. Phylogenetic tree and single nucleotide polymorphism (SNP) assessment indicated that the strain identified in Patient B and the simple resuscitation bag belonged to the same phylogenetic clade, but with more than 14 SNP differences. The other five patients and environmental strains constituted a separate clade, exhibiting closer phylogenetic relationships among certain patient strains and environmental strains, as well as among the environmental strains themselves. No new infection cases have occurred since the implementation of preventive and control measures.

The CRAB infections in this department did not constitute a nosocomial infection outbreak; however, attention should be directed toward clonal transmission driven by mobile genetic elements. The urine bag drainage valve switch is identified as a potential transmission risk point that warrants special attention. It is imperative to enhance nosocomial infection prevention and control measures, including environmental disinfection, hand hygiene, and patient isolation.