An Irish outbreak of New Delhi metallo-β-lactamase (NDM)-1 carbapenemase-producing Enterobacteriaceae: increasing but unrecognised prevalence

Background Carbapenemase-producing Enterobacteriaceae (CPE) can cause healthcare–associated infections with high mortality rates. New Delhi metallo-beta-lactamase-1 (NDM-1) is amongst the most recently discovered carbapenemases. Aim To report the first outbreak of NDM-1 CPE in Ireland, including microbiological and epidemiological characteristics, and assessing the impact of infection prevention and control measures. Methods Retrospective microbiological and epidemiological review. Cases were defined as patients with a CPE positive culture. Contacts were designated as roommates or ward mates. Findings This outbreak involved ten patients, with a median age of 71 years (range 45-90 years), located in three separate but affiliated healthcare facilities. One patient was infected (the index case); the nine others were colonised. Nine NDM-1-producing Klebsiella pneumoniae, a NDM-1-producing Escherichia coli and a K. pneumoniae carbapenemase (KPC)-producing Enterobacter cloacae were detected between week 24 2014 and week 37 2014. Pulsed field gel electrophoresis demonstrated similarity. NDM-1 positive isolates were meropenem resistant with MICs ranging from 12 to 32 μg/ml. All were tigecycline susceptible (MICs ≤1 μg/ml). One isolate was colistin resistant (MIC 4.0 μg/ml; mcr-1 gene not detected). In 2015, four further NDM-1 isolates were detected. Conclusions The successful management of this outbreak was achieved via the prompt implementation of enhanced infection prevention and control practices to prevent transmission. These patients did not have a history of travel outside of Ireland, but a number had frequent hospitalisations in Ireland, raising concerns regarding the possibility of increasing but unrecognised prevalence of NDM-1 and potential decline in value of travel history a marker of colonisation risk.