A nosocomial foodborne outbreak of a VIM carbapenemase-expressing Citrobacter freundii

Abstract

Background

A foodborne outbreak of VIM carbapenemase-expressing Citrobacter freundii (CPC) occurred between February and June 2016 at a major university hospital in Germany.

Methods

An explosive increase of CPC isolated from rectal swabs of patients during weekly routine screening led to the declaration of an outbreak. A hospital-wide prevalence screening was initiated as well as screening of all patients on admission and before transfer to another ward, and canteen staff, patient rooms, medical and kitchen inventory and food. Swabs were streaked out on selective plates. All CPC isolates were analysed by mass spectrometry and selected isolates by whole-genome sequencing.

Results

In total, 76 mostly unrelated cases in different wards were identified. The CPC was isolated from retained samples of prepared vegetable salads and puddings and from a mixing machine used to prepare them only after an overnight culture. The immediate ban on serving potential source food resulted in a sharp decline and finally disappearance of novel cases. Repeated testing of pre-sliced vegetables showed a high degree of contamination with C. freundii without a carbapenemase, indicating a possible source.

Conclusions

This report demonstrates that an explosive increase in carbapenemase-expressing Enterobacteriaceae contamination may be caused by a food-borne source, and suggests that pre-sliced vegetables have to be taken into account as a putative pathogen repository. It also underlines the importance of appropriate cooling, transport, re-heating and distribution of meals and indicates that probing of non-organic surfaces is limited by low sensitivity, which may be increased by additional overnight cultivation in appropriate media.