Researchers analyzed mandatory notification data on invasive listeriosis cases in Germany from 2010 to 2019 to describe time trends, case-fatality rates, demographic distribution, clinical and diagnostic characteristics, and geographic trends.

In total, 5,576 listeriosis cases were reported during the 10-year period; 5,064 were not pregnancy associated and 486 were pregnancy associated involving mothers and newborns.

The lowest annual incidence was in 2011 and the highest in 2017. There was a steady increase from 2011 to 2017, but the rate in 2019 was lower than previous years. Successfully identifying and controlling large outbreaks, especially after whole genome sequencing-based surveillance was introduced, could explain why the rise ended after 2017, said researchers in the journal Emerging Infectious Diseases.

Exceptionally high numbers were reported in the third quarters of 2016, 2017, and 2018 due to large-scale outbreaks.

Aging population and meat popularity
Among the 5,064 non-pregnancy associated patients, 2,032 were female and 3,855 were over 65 years of age. Annual median age of patients increased from 72 years old in 2010 to 77 in 2019.

Most non-pregnant patients were hospitalized and 658 died. Listeriosis was the main cause of death for 324 people and a contributing factor for 280. This makes a patient fatality rate of 13 percent.

A total of 32 fetal losses and 26 neonatal deaths resulted in a patient fatality rate of 19 percent for pregnancy-associated cases.

The patient fatality rate in the study is lower than the 15.6 percent for all of Europe and 21 percent in the United States found in other work. Scientists said this could be because deaths occurring long after original disease notifications were not reported to public health departments.

Surveillance data from the U.S. indicate more listeriosis among women and higher proportions of pregnancy-associated cases than in the German study. One explanation might be that, in Germany, meat products are more often eaten by men and are often outbreak vehicles, whereas in the U.S. several outbreaks were caused by food of non-animal origin or cheese.

An aging population in Germany may partially explain the increase in listeriosis and the median age of patients. Listeriosis is also highly associated with documented immunosuppressive conditions, according to the research.

Researchers said people with these risk profiles should be targeted in information campaigns about how to safely consume RTE foods and avoid certain types of cheeses, meat products, and smoked or graved, also known as cured, fish.

Another study, looking at investigational tracing as a method for outbreak investigation, revealed that between 2016 and 2020, about 600 to 700 listeriosis cases were reported annually in Germany. Since 2018, the increased use of WGS methods has revealed more outbreak clusters although the annual number of cases has remained stable.

(To sign up for a free subscription to Food Safety News, click here.)