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 .