Background: A. baumannii is a common nosocomial pathogen known for its high transmission potential. A high\nrate of carbapenem-susceptible Acinetobacter calcoaceticus-Acinetobacter baumannii (ACB)-complex in clinical\nspecimens led to the implementation of a pathogen-based surveillance on a 32-bed surgical intensive care unit\n(SICU) in a German tertiary care centre.\nMethods: Between April 2017 and March 2018, ACB-complex isolates with an epidemiological link to the SICU\nwere further assessed. Identification to the species level was carried out using a multiplex PCR targeting the gyrB\ngene, followed by RAPD, PFGE (ApaI) and whole genome sequencing (WGS, core genome MLST, SeqSphere+\nsoftware, Ridom). Additional infection prevention and control (IPC) measures were introduced as follows:\nepidemiological investigations, hand hygiene training, additional terminal cleaning and disinfection incl. UV-light,\nscreening for carbapenem-susceptible A. baumannii and environmental sampling. Hospital-acquired infections were\nclassified according to the CDC definitions.\nResults: Fourty four patients were colonized/infected with one or two (different) carbapenem-susceptible ACB-complex\nisolates. Fourty three out of 48 isolates were classified as hospital-acquired (detection on or after 3rd day of admission).\nNearly all isolates were identified as A. baumannii, only four as A. pittii. Twelve patients developed A. baumannii infections.\nGenotyping revealed two pulsotype clusters, which were confirmed to be cgMLST clonal cluster type 1770 (n = 8\npatients) and type 1769 (n = 12 patients) by WGS. All other isolates were distinct from each other. Nearly all\ntransmission events of the two clonal clusters were confirmed by conventional epidemiology. Transmissions stopped\nafter a period of several months. Environmental sampling revealed a relevant dissemination of A. baumannii, but only a\nfew isolates corresponded to clinical strains. Introduction of the additional screening revealed a significantly earlier\ndetection of carbapenem-susceptible A. baumannii during hospitalization.\nConclusions: A molecular and infection surveillance of ACB-complex based on identification to the species level,\nclassic epidemiology and genotyping revealed simultaneously occurring independent transmission events and clusters\nof hospital-acquired A. baumannii. This underlines the importance of such an extensive surveillance methodology in\nIPC programmes also for carbapenem-susceptible A. baumannii.
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