Large Nationwide Outbreak of Invasive Listeriosis Associated with Blood Sausage, Germany, 2018-2019

Abstract

Invasive listeriosis is a severe foodborne infection in huÂmans and is difficult to control. Listeriosis incidence is inÂcreasing worldwide, but some countries have implemented molecular surveillance programs to improve recognition and management of listeriosis outbreaks. In Germany, routine whole-genome sequencing, core genome multiloÂcus sequence typing, and single nucleotide polymorphism calling are used for subtyping of Listeria monocytogenes isolates from listeriosis cases and suspected foods. DurAîng 2018-2019, an unusually large cluster of L. monocytoÂgenes isolates was identified, including 134 highly clonal, benzalkonium-resistant sequence type 6 isolates collected from 112 notified listeriosis cases. The outbreak was one of the largest reported in Europe during the past 25 years. Epidemiologic investigations identified blood sausage conÂtaminated with L. monocytogenes highly related to clinical isolates; withdrawal of the product from the market ended the outbreak. We describe how epidemiologic investigaÂtions and complementary molecular typing of food isolates helped identify the outbreak vehicle.