German authorities are investigating almost 60 cases of Listeria in the south and west of the country.

The Robert Koch-Institut (RKI) said 57 isolates could be allocated to notified cases of listeriosis in Germany and it believes there is a probable epidemiological link between the infections.

RKI and the Austrian Agency for Health and Food Safety (AGES) have repeatedly identified Listeria monocytogenes strains of the molecular serogroup IVb from human infections with the same or closely related core genome multi locus sequence typing (cgMLST) types since August this year.

In the isolates studied, an identical cluster type (CT) 4465 and the closely related CT7353 were determined, according to RKI. Single nucleotide polymorphism (SNP) analyzes confirmed the close phylogenetic relationship of the isolates.

Last year, Germany reported 770 cases of Listeriosis compared to 704 in 2016. Since 2011 the number of infections has been rising steadily in the country.

One case has been reported in France but the person had exposure in Germany.

Officials are interviewing patients as part of attempts to find the food source of the outbreak. So far no isolates have been found with the same cluster types from food.

An RKI spokeswoman told Food Safety News that the outbreak is focused in Baden-Württemberg and North Rhine-Westphalia.

“Some patients were tested in Austria but reported to authorities in Germany. (The outbreak) was detected applying whole genome sequencing to isolates sent to the reference labs,” she said.

“First illness onset is May 2018, the outbreak is probably ongoing. Hypothesis-generating interviews of patients are ongoing.

“There is one case reported in France with exposure in Germany. As far as we know based on the molecular type and epidemiological evidence this outbreak is not related to other outbreaks.”

Germany has been affected by other Listeria outbreaks this year including one linked to ready-to-eat salmon products, such as cold-smoked and marinated salmon that has 12 cases and four deaths.

The country reported the most recent case in this outbreak in May 2018 and has five infections in total. Illnesses due to Listeria monocytogenes sequence type (ST) 8 have also been recorded in Denmark and France since 2015.

The European Food Safety Authority (EFSA) is also working on a report of two multi-country clusters of Listeria monocytogenes infections linked to salmon consumption which is due to be published this month.