Ms Alexandra Marmor1,4, Dr Kathryn Daveson1,2, Associate Professor David Harley3, Dr Karina Kennedy1,2
1Australian National University, Acton, Australia,
2The Canberra Hospital, Garran, Australia,
3Queensland Centre for Intellectual and Developmental Disability, Mater Research Institute, University of Queensland, Raymond Terrace, Australia,
4Australian Government Department of Health, Woden, Australia
Carbapenemase-producing Enterobacteriaceae (CPE) pose a serious threat to the effectiveness of last-line antimicrobial agents in Australia. In 2014, two genetically linked cases of 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 of CPE between 2012 and 2016 were identified from the ACT Pathology laboratory information system. Whole-genome sequencing was performed retrospectively on 83% of isolates. We investigated two multilocus sequence type clusters using epidemiological, molecular and environmental evidence.
Seventy-two cases were identified, with 90% of isolates containing blaIMP genes. Enterobacter cloacae complex and Citrobacter freundii were most frequently detected, and based on multi-locus sequence types (STs), were implicated in two outbreaks each spanning over three years. The E. cloacae complex ST24 outbreak consisted of seven cases, including the two linked cases identified in 2014. The C. freundii ST8 outbreak consisted of ten cases. Both outbreaks most likely originated in the haematology ward and spread via environmental reservoirs and undetected carriers there, in the intensive care unit, and in five other wards.
Epidemiological and molecular evidence indicate transmission at TCH is more extensive than previously understood. Prevention and control measures must address asymptomatic carriage and persistence in the hospital environment. The value of WGS in CPE outbreak investigation would be increased by using methods that account for gene transfer between Enterobacteriaceae species.
Alex is a Master of Applied Epidemiology scholar from the Australian National University, on placement with the Australian Government Department of Health. She is a Registered Nurse with experience in rural and remote emergency and primary health care, Indigenous health, and in medical and surgical nursing at the Canberra Hospital.