Outbreak Investigation of Extensively Drug-Resistant Acinetobacter baumannii of ST2 in the Intensive Care Unit of a Lebanese Hospital

Background: The aim of the study is to investigate an XDR Acinetobacter baumannii outbreak in the ICU of a tertiary hospital in Lebanon. Materials and Methods: A total of 39 swabs were sampled from the ICU room (n=34; environmental surfaces and n=5; clinical A. baumannii swabs from admitted patients). The strains were selected using Muller Hinton (MH) agars supplemented with 4 µl/mL of meropenem. Species identification and antibiotic susceptibility profiles were determined using MALDI-TOF MS and broth microdilution assays, respectively. Long-read whole-genome sequencing (WGS) was performed on the positive swabs (n=13).  Clonal relatedness was assessed by multilocus sequence typing (MLST), and genomes were compared through SNP-based phylogeny. Results and Discussion: Thirteen isolates were XDR A. baumannii, of which 8 were from environmental swabs. WGS revealed the presence of chromosomally located blaOXA-23 gene in all isolates. MLST analysis showed that all strains belong to ST2 international clone. The SNP-based phylogeny suggested that the outbreak originated from multiple ST2 isolates clustering into two main clades (A and B). Clade A confined 5 strains, having only 0 to 1 SNPs when compared to each other. Whereas, clade B had 7 strains that differed by 1 to 139 SNPs when compared to each other and 2248 to 2387 when compared with the reference genome LBN-30 in clade A. Conclusion: We report a continuous and persistent nosocomial outbreak of XDR A. baumannii in the ICU of a Lebanese hospital, despite the implementation of conventional infection control practices. This prolonged circulation of this strain indicates the necessity for extensive systematic screening for both environmental and patient reservoirs, as well as the need for alternative disinfection strategies.​