Abstract
Invasive listeriosis is a severe foodborne infection in humans and is difficult to control. Listeriosis incidence is increasing 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 multilocus sequence typing, and single nucleotide polymorphism calling are used for subtyping of Listeria monocytogenes isolates from listeriosis cases and suspected foods. During 2018–2019, an unusually large cluster of L. monocytogenes 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 contaminated with L. monocytogenes highly related to clinical isolates; withdrawal of the product from the market ended the outbreak. We describe how epidemiologic investigations and complementary molecular typing of food isolates helped identify the outbreak vehicle.
Highlights
Invasive listeriosis is a severe foodborne infection in humans and is difficult to control
We describe an exceptionally large nationwide outbreak that included 134 laboratory-confirmed L. monocytogenes isolates from 112 patients with epidemiologic investigations and complementary WGSbased typing of food isolates identifying the outbreak vehicle
To identify the outbreak clone among all incoming serogroup IVb isolates, we developed a clone-specific PCR (Appendix)
Summary
Invasive listeriosis is a severe foodborne infection in humans and is difficult to control. L. monocytogenes forms hard-to-remove biofilms in food-processing plants, can acquire tolerance to sanitizers, and multiplies even at temperatures used for refrigeration [8] These properties complicate efficient prevention of L. monocytogenes contaminations in different types of ready-to-eat products, including dairy, meat, and fish, and in fruits and vegetables, all of which have been vehicles for listeriosis outbreaks in the past [9,10,11,12]. Listeriosis outbreaks can be protracted and last for several years [16], making it difficult to correctly identify affected patient groups and the common source of infection. Since August 2019, Spain has been experiencing another large listeriosis outbreak [23], but the scientific evaluation of this outbreak is ongoing
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