L isteria monocytogenes infections are primarily foodborne and cause gastrointestinal disease or invasive syndromes among infected persons (1). Because L. monocytogenes is an intracellular pathogen and because invasive listeriosis is the primary manifestation in diagnosed listeriosis, persons with defi cient cell-mediated immunity are at increased risk for its symptoms, including sepsis and meningitis. In addition, infection during pregnancy can lead to chorioamnionitis and fetal infection that can result in miscarriage and stillbirth even 2 months after the mother is exposed. One study found that 44% of patients with non-pregnancyassociated (NPA) listeriosis in Germany had received immunosuppressive therapy ≤3 months before illness onset and another 28% had a coexistent immunocompromising illness, such as diabetes (2). Testing for bacteria in blood cultures or cerebrospinal fl uid (CSF) is recommended for diagnosis.Listeria is ubiquitous in the environment and can produce biofi lms in the food production environment and thus contaminate ready-to-eat (RTE) products, which are typically consumed raw or without further processing. Listeria species grow during shelf life, even at low temperatures, and multiply to concentration levels that make invasive listeriosis and outbreaks more likely. For these reasons, it is suspected that L. monocytogenes exposure is very common but the disease rare. However, in recent years several large outbreaks have been reported in Germany (3-7).
The StudyWe analyzed mandatory notifi cation data about invasive listeriosis cases in Germany during 2010-2019 to describe time trends, case-fatality rates, demographic distribution, clinical and diagnostic characteristics, and geographic trends (Appendix, https://wwwnc. cdc.gov/EID/article/27/9/21-0068-App1.pdf). In total, 5,576 listeriosis cases were reported during the 10year study period; 5,064 (91%) of those were NPA and 486 (9%) were pregnancy associated, 241 in mothers and 245 in newborns. Information on disease manifestation was not transmitted for 26 cases. The lowest annual incidence was in 2011 (0.41/100,000 residents) and the highest in 2017 (0.93/100,000 residents); the average for 2010-2019 was 0.69/100,000 residents. We observed a steady increase in cases during 2011-2017, but incidence in 2019 was lower than in previous years. Exceptionally high numbers were reported in the third quarters of 2016, 2017, and 2018 (Figure 1).Among the 5,064 NPA listeriosis case-patients, 2,032 (40%) were female and 3,855 (76%) were >65 years of age (Table 1). Listeriosis among adolescents and children other than newborns is rare (37 cases). Incidence in adults 18-44 years of age is <0.1/100,000 residents, in contrast with incidence among adults ≥85 years of age: 3.99/100,000 residents for men and 2.08/100,000 residents for women. Annual median age of case-patients increased steadily from 72 years of age in 2010 to 77 years of age in 2019.Sources for testing samples included CSF (657, 13%), blood (4,097, 81%), and material from other usually steril...