Invasive listeriosis outbreaks and salmon products: a genomic, epidemiological study

ABSTRACT

Invasive listeriosis, caused by Listeria (L.) monocytogenes, is a severe foodborne infection, especially for immunocompromised individuals. The aim of our investigation was the identification and analysis of listeriosis outbreaks in Germany with smoked and graved salmon products as the most likely source of infection using whole-genome sequencing (WGS) and patient interviews. In a national surveillance programme, WGS was used for subtyping and core genome multi locus sequence typing (cgMLST) for cluster detection of L. monocytogenes isolates from listeriosis cases as well as food and environmental samples in Germany. Patient interviews were conducted to complement the molecular typing. We identified 22 independent listeriosis outbreaks occurring between 2010 and 2021 that were most likely associated with the consumption of smoked and graved salmon products. In Germany, 228 cases were identified, of 50 deaths (22%) reported 17 were confirmed to have died from listeriosis. Many of these 22 outbreaks were cross-border outbreaks with further cases in other countries. This report shows that smoked and graved salmon products contaminated with L. monocytogenes pose a serious risk for listeriosis infection in Germany. Interdisciplinary efforts including WGS and epidemiological investigations were essential to identifying the source of infection. Uncooked salmon products are high-risk foods frequently contaminated with L. monocytogenes. In order to minimize the risk of infection for consumers, food producers need to improve hygiene measures and reduce the entry of pathogens into food processing. Furthermore, susceptible individuals should be better informed of the risk of acquiring listeriosis from consuming smoked and graved salmon products.

KEYWORDS:

• Listeriosis
• salmon products
• foodborne outbreaks
• public health
• molecular surveillance

Acknowledgements

We are very grateful to Andrea Thürmer and Robin Redel for genome sequencing, to Simone Dumschat, Marett Splett, and Isabel Knittel-Fischer for excellent technical assistance and the local and federal public health and food safety authorities for their strong support in the outbreak investigations. Authors’ contribution: Writing – Original Draft: R.L. and H.W.; Writing – Review & Editing: S.L., S.H., M.A., A.H., A.P., S.K., S.A.D., K.S., and A.F.; Conceptualization: R.L., A.F., H.W., and K.S.; Epidemiological investigation: R.L. and A.H.; Formal Analysis: R.L., S.H., S.L., S.K., M.A., A.P., S.A.D., and A.H.; Data curation: S.H., A.H., S.L., S.K., and M.A.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by Robert Koch Institute (RKI), the German Federal Institute for Risk Assessment (BfR), and a grant of the Federal Ministry of Health (GE 2016 03 26) in the framework of the German Research Platform for Zoonoses. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.