One-year molecular surveillance of carbapenem-susceptible A. baumannii on a German intensive care unit: diversity or clonality

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