Finland reported a record number of Listeria infections this past year with the figure almost twice as high as 2019.

The 93 Listeria infections in 2020 were nearly double the 50 in the year before and the largest annual total ever reported to the National Infectious Diseases Register. Almost 80 infections were recorded in 2018 and 90 in 2017.

Nearly all bacterial infections decreased significantly in 2020 from mid-March because of measures put in place because of the coronavirus pandemic, according to data published by the Finnish Institute for Health and Welfare (THL).

The THL is responsible for the monitoring, prevention and control of infectious diseases in Finland. Physicians and laboratories report findings on infectious diseases to the National Infectious Diseases Register maintained by the agency.

Listeria infections have increased since 2009. In Finland, risky foods include dry-cured and cold-smoked fish products. In total, 58 percent of patients were more than 70 years of age and 47 were men.

Campylobacter is the most common bacterial cause of gastrointestinal infections in Finland. In 2020, 2,074 infections were reported to the register. This is just under half of what it was in 2019, but the share of infections of domestic origin was higher than previous years.

Most infections were reported in people aged 45 to 54 years old and incidence was highest in July.

“Last year, travel restrictions may have increased the share of domestic infections, but their number has already been on the rise since 2010. More information is still needed on the origin of infections so that prevention measures can be better targeted,” said Tuula Hannila-Handelberg, chief physician at the Finnish Institute for Health and Welfare.

Listeria outbreak investigations
Suspected food and waterborne outbreaks were sent to a system overseen by THL and the Finnish Food Authority (Ruokavirasto). In total, 58 notifications were made compared to 81 in 2019. Several other infection clusters were also identified.

During 2020, 10 different listeriosis clusters were investigated. In one, 23 people fell ill from 2016 to 2020 across Finland. An investigation found an epidemiological and microbiological association between illness and a meat company. Isolates from patients were similar to strains isolated from the products of a meat establishment in 2017 and 2020. Listeria had been repeatedly detected in the plant’s products and production environment in 2019 and 2020.

In another infection cluster 14 people fell sick, also from 2016 to 2020. Patient samples were similar to Listeria strains isolated from the products of another meat factory that were typed in 2020. Analysis found an epidemiological and microbiological link between the illness of three patients and this firm.

In a third outbreak, 21 people became ill from 2017 to 2020 across Finland. Patient isolates were similar to strains found in 2020 from lettuce and salad of one company. No Listeria was found during environmental sampling of the factory.

An outbreak of Yersinia enterocolitica in early 2020 involved 20 people and was linked to chopped iceberg lettuce. A rare Salmonella Kedougou outbreak affected eight people and was caused by contaminated chopped zucchini from Spain that was put in a salad.

Decline for other causes of illness
The number of Salmonella cases continued to decline and was 522 compared to 1,182 in 2019.

Domestic Salmonella infections were caused by 37 different serotypes. Of these, the four most common were Typhimurium, Group B, Saintpaul, and Enteritidis. They caused 64 percent of infections.

For enterohaemorrhagic E. coli (EHEC), 175 cases were reported to the registry compared to 311 in 2019.

Incidence was highest among those aged up to 4 years old. In total, 125 infections were classed as domestic. Strains came from 37 O-serogroups, the most common being O157, O103 and O26.

A total of 865 cases of norovirus were reported versus 3,388 in 2019. They mainly fell sick between January and May. Cases occurred in all age groups, but slightly more than half were over 75 years old and women accounted for 59 percent of infections.

In 2020, there were 403 cases of Yersinia enterocolitica compared to 485 in 2019. Incidence was highest in those aged 25 to 29.

A total of 41 Shigella patients were reported in 2020, down from 154 in 2019, and eight were domestic infections. The most common types were Shigella flexneri and Shigella sonnei.