Meinel^1,2, R. Kuehl³, R. Zbinden⁴, V. Boskova⁵, C. Garzoni⁶, M. Dolina⁷, B. Blümel⁸, S. Tschudin³, AF. Widmer³, JA. Bielicki⁹, U. Heininger⁹, R. Konrad², A. Berger², V. Hinic¹, D. Goldenberger¹, A. Blaich¹, T. Stadler⁵, M. Battegay³, A. Sing², A. Egli¹

¹ Clinical Microbiology, University Hospital Basel, Switzerland, ² National Consiliary Laboratory on Diphtheria, Oberschleissheim, Germany, ³ Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Switzerland, ⁴ Institute for Medical Microbiology, University Zurich, Switzerland, ⁵ Computational Evolution, ETH Zurich, Switzerland, ⁶Department of Internal medicine and Infectious Diseases, Clinica Luganese, Switzerland, ⁷Clinical Microbiology, EOLAB, Bellinzona, Switzerland ⁸ Institute of Medical Microbiology and Hygiene, University Medical Centre Freiburg, Germany ⁹ Paediatric Infectious Diseases, University of Basel Children’s Hospital, Switzerland

Background: Toxigenic Corynebacterium diphtheriae is an important and potential fatal threat to patients and public health. During the current dramatic influx of refugees in Europe, we used whole genome sequencing to characterise a suspected outbreak of C. diphtheriae among refugees.
Methods: After conventional culture, we identified C. diphtheriae isolates using MALDI-TOF mass-spectrometry. Whole genome sequencing was performed on a MiSeq Illumina platform with >70x coverage, 2x250bp read length.
Results: Twenty cases of cutaneous C. diphtheriae in refugees from East African countries and Syria identified between April and August 2015 were included. Patients presented with wound infections shortly after arrival in Switzerland and Germany. Toxin production was detected in 11/20 (55%) isolates. Whole genome sequencing-based typing revealed the relatedness between isolates using Neighbour joining algorithms. We detected three separate clusters among these epidemiologically related refugees. Although the isolates within a cluster showed strong relatedness, they were not absolutely identical.
Conclusions: Toxigenic C. diphtheriae associated wound infections may currently be observed more frequently in Europe, perhaps due to refugees travelling under poor hygienic conditions. Close genetic relatedness of C. diphtheriae isolates from 20 refugees with wound infections indicates likely transmission between affected patients. However, the diversity within each cluster and the phylogenic time-tree analysis suggest that transmission happened several months ago, most likely outside Europe. Whole genome sequencing offers the potential to describe outbreaks in very high resolution and is a helpful tool in infection tracking and identification of transmission routes