Longitudinal surveillance and transmission of Acinetobacter baumannii using whole genome sequencing-a tale of two hospitals.

Objective: Acinetobacter baumannii is known to cause global outbreaks and routine surveillance to prevent nosocomial transmission has historically been limited. A longitudinal surveillance study of Acinetobacter isolates using whole genome sequencing (WGS) and whole genome multilocus sequence typing (wgMLST) was performed to map the distribution of sequence types (STs) and intrahospital transmission.

Methods: All Acinetobacter clinical isolates were collected in two hospitals (H1, H2) from fifteen units between 2017 and 2021 in Southeast Michigan and analyzed. The isolates were subjected to WGS using the NextSeq instrument (Illumina). The contigs were de novo assembled using SPAdes (v3.7.1) and wgMLST analysis was performed using BioNumerics software v7.6. Minimum spanning tree (MST) and dendrograms were created to map distribution of STs and putative transmissions.

Results: ST2^Pas was the most prevalent in both hospitals (H1:47.2% and H2:59.7%), followed by ST406^Pas (H1:11.1%, H2:8%). ST15^Pas (H1:9.7%) was only found in H1. Transmission was mapped for ST2^Pas, ST406^Pas (H1, H2), and ST15^Pas for H1 and mainly located in the ICU settings.

Conclusions: Presence of several STs (ST2^Pas, ST406^Pas, and ST15^Pas) prevalent from both hospitals suggest that these are common circulating strains in the area. Sporadic transmission events mainly in the ICU settings in both hospitals (H1 and H2) were noted indicating attention to enhanced infection prevention and control measures. Given that Acinetobacter infections are predominantly hospital acquired, an effective surveillance plan incorporating WGS and wgMLST may improve the ability to identify and track trends rapidly, implement effective infection control intervention, and reduce healthcare-associated infections (HAIs).