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. 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 Mueller Hinton (MH) agars supplemented with 4 µg/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 anddiscussion: Thirteen isolates were XDRA.baumannii,ofwhich8were 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. Core-genome SNP analysis using LBN-30 as a reference, resolved the 13 genomes intotwo outbreak clades and oneunrelated genome: Clade A (n=5, 0–1 SNPs from the reference), clade B (n=7, 2248–2387 SNPs from the reference), and LBN-38,the singleton, (2145 SNPs from the reference). 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. The aim of the study is to investigate an XDR Acinetobacter baumannii outbreak in the ICU of a tertiary hospital in Lebanon. 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 Mueller Hinton (MH) agars supplemented with 4 µg/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 bla OXA-23 gene in all isolates. MLST analysis showed that all strains belong to ST2 international clone. Core-genome SNP analysis using LBN-30 as a reference, resolved the 13 genomes into two outbreak clades and one unrelated genome: Clade A (n=5, 0–1 SNPs from the reference), clade B (n=7, 2248–2387 SNPs from the reference), and LBN-38,the singleton, (2145 SNPs from the reference). 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.