Tracing and transmission analysis of a nosocomial infection event caused by hypervirulent Acinetobacter baumannii / 中华临床感染病杂志

ABSTRACT

Objective:To trace and identify the source and the transmission vector of a nosocomial infection event caused by hypervirulent Acinetobacter baumannii. Methods:Nine strains of carbapenem-resistant Acinetobacter baumannii (CRAB) isolated from respiratory general ward and respiratory intensive care unit in Shenzhen People’s Hospital from July to August 2018 were collected. Environmental specimens such as ward environmental objects and medical staff’s hands were also collected. Vitek 2 was used for identification of bacterial species and drug susceptibility testing; Illuinam HiSeq 2500 platform, Staramr, Ridom SeqSphere+ were used for whole genome sequencing, drug resistance gene detection and multi-locus sequence typing (MLST); and IQ-Tree software, BEAST2 software package and SCOTTI software were used to construct phylogenetic tree and propagation path map. At the same time, the virulence of pathogenic bacteria was detected by mouse pneumonia model. Results:The 9 isolated CRAB strains were all ST2 type, all carried the carbapenem-resistant gene blaOXA-23, and the capsular types were KL49, KL3, KL77 and KL2, respectively. One of the CRAB strains isolated from removable ventilator screen was ST2 type and KL49 type capsule. Phylogenetic tree analysis showed that the environmental isolates were located in the same branch as 5 CRABs, and the transmission path map showed that these 5 CRABs were also located in the same transmission chain. Five strains of CRAB were involved in four lethal cases, and in vivo experiments in mice confirmed that the strains causing lethal infection had a hypervirulent phenotype. Conclusions:Highly virulent Acinetobacter baumannii can colonize the surface of mobile medical equipment, and sharing these equipment may lead to nosocomial spread of pathogens. The use of new propagation path analysis tools has certain reference significance for the investigation of propagation events.