Transmission of carbapenemase-producing Enterobacter in Ontario, Canada: A Retrospective Genomic Analysis

Carbapenemase-producing <i>Enterobacter</i> (CP-Ent) are the third most prevalent species of CP-<i>Enterobacteriaceae</i> worldwide and exhibit greater strain diversity than other CP-species. This study aimed to describe the genomic epidemiology of CP-Ent in south-central Ontario, Canada. CP-Ent isolates collected from colonised/infected patients identified by population-based surveillance in Toronto/Peel Region, Canada (2007-2020), sink/shower drains in 12 regional hospitals (2016-2019), and five municipal wastewater treatment plants (2015, 2017) were analysed to assess relationships between patient and environmental CP-Ent. Clinical data were collected by chart review/patient interview. CP-Ent isolates were sequenced by Illumina. Genomic analysis included Snippy, IQ-Tree, and ClonalFrameML; ≤ 20 single-nucleotide variant differences defined strains. CP-Ent colonisation/infection incidence increased from 2007-2020. Overall, 3.5% of sink/shower drains and 22% of municipal wastewater cultures yielded CP-Ent. Patient and sink/shower drain isolates were similar in species and carbapenemases produced; municipal wastewater isolates were distinct. Forty-one of 116 patients (35%) belonged to 15 transmission clusters: 5/15 (33%) included drain isolates, and 32/41 (78%) patients were linked to others in the same hospital, including 22 (54%) linked by stays in the same ward. Patients were more likely to be linked by ward exposure at different times versus the same time in wards with sink/shower drains yielding CP-Ent versus those without (13/19 vs 2/23, p=&lt;.001). Despite transmission control efforts, a significant proportion of CP-Ent are part of hospital transmission clusters; sink/shower drains may be implicated in transmission. It is likely that undetected patients, drains and/or other reservoirs contribute to CP-Ent transmission in the studied population.