Hospital outbreak caused by linezolid resistant Enterococcus faecium in Upper Austria

Background Enterococcus faecium is part of the human gastrointestinal flora but may act as opportunistic pathogen. Environmental persistence, high colonization capability and diverse intrinsic and acquired resistance mechanisms make it especially successful in nosocomial high-risk settings. In March 2014, an outbreak of Linezolid resistant Enterococcus faecium (LR Efm ) was observed at the hematooncology department of a tertiary care center in Upper Austria. Methods We report on the outbreak investigation together with the whole genome sequencing (WGS)-based typing results including also non-outbreak LR Efm and susceptible isolates. Results The 54 investigated isolates could be divided in six clusters based on cgMLST. Cluster one comprised LR Efm isolates of genotype ST117 and CT24, which was identified as the causative clone of the outbreak. In addition, the detection of four other clusters comprising isolates originating from hematooncology patients but also at other hospitals, pointed to LR Efm transmission between local healthcare facilities. LR Efm patients ( n = 36) were typically at risk for acquisition of nosocomial pathogens because of immunosuppression, frequent hospitalization and antibiotic therapies. Seven of these 36 patients developed LR Efm infection but were successfully treated. After termination of the initial outbreak, sporadic cases occurred despite a bundle of applied outbreak control interventions. Conclusions WGS proved to be an effective tool to differentiate several LR Efm clusters in an outbreak. Active screening for LR Efm is important in a high-risk setting such as hematooncology, where multiple introductions are possible and occur despite intensified infection control measures.