Anca Rath (Regensburg / DE), Joachim Hahn (Regensburg / DE), Matthias Grube (Regensburg / DE), Aila Caplunik-Pratsch (Regensburg / DE), Anja Eichner (Regensburg / DE), Jürgen Fritsch (Regensburg / DE), Wulf Schneider-Brachert (Regensburg / DE), Bärbel Kieninger (Regensburg / DE)
Background
Genome-oriented outbreak management (OM) is still uncommon in routine infection control. The strain dynamics of vancomycin-resistant Enterococcus faecium (VRE), however, often complicate the distinction between real- and pseudo-outbreaks. This project analyzes how the same outbreak situations unravel, and how high the efficiency of OM is, when using strain-typing methods with increasing resolution of genetic data.
Methods
In 2022, prolonged VRE outbreaks affected 47 patients at our oncology department. OM interventions were done twice (June and October), dividing the events into three phases. 47 isolates from 44 patients (including two isolates with different van-genotypes for three patients) were collected during January 2022-February 2023, and characterized using MALDI-ToF, in-house vanAB-PCR, and short-read whole-genome sequencing (WGS). Subsequently, the different levels of characterization were used to evaluate the outbreak dynamics and OM efficiency.
Results
Epidemiological data suggests that the VRE outbreak during Phase 1 was terminated by OM, whereas it did not affect Phase 2. While WGS confirmed a monoclonal outbreak of ST1299/CT1903/vanA during Phase 1, Phase 2 was caused by a polyclonal outbreak. ST1299/CT1903/vanA was also most common among VRE/vanA during Phase 2, and two isolates were closely related to isolates from Phase 1. The prolonged hospitalization of patients from Phase 1 appears to be the most probable reason. The remaining ST1299/CT1903/vanA isolates are split in two clusters, suggesting VRE introduction on two further occasions. Although clusters of VRE/vanB were also identified during Phase 2, these were small-sized. The spread of both VRE/vanA and VRE/vanB outbreak strains in Phase 2 was also promptly interrupted by OM according to WGS data and cgMLST. The outbreak suspicion in Phase 3 was not confirmed.
Conclusions
Our genome-oriented approach to infection control clearly demonstrates that the success of OM for VRE is feasible, but can only be evaluated using WGS. Without this, the extent of clinical outbreaks can be grossly overestimated during routine investigations, whereas OM efficiency is falsely questioned.