Two carbapenemase-producing Enterobacteriaceae outbreaks detected retrospectively by whole-genome sequencing at an Australian tertiary hospital.

In 2014, two genetically-linked cases of carbapenemase-producing Enterobacteriaceae (CPE) were detected at the Canberra Hospital (TCH), prompting an investigation and response that appeared to contain transmission. We report a 2017 retrospective investigation into cases of CPE in the Australian Capital Territory (ACT) that aimed to identify clusters and transmission mechanisms. Cases detected between 2012 and 2016 were identified from the hospital laboratory information system. Whole-genome sequencing (WGS) was performed retrospectively on stored isolates. Seventy-two cases were identified, with nearly 90% of isolates containing blaIMP genes. Using multilocus sequence type (ST) data, we identified two small outbreaks of CPE containing blaIMP-4 (Enterobacter cloacae complex ST24, n = 7; Citrobacter freundii ST8, n = 10), each spanning over three years. Epidemiological and environmental evidence implicate environmental reservoirs and carriers undetected by routine infection prevention and control investigations.