Frozen tomato cubes were behind a Salmonella Typhimurium outbreak in Finland in 2021, according to a new study.

It is thought to be the first outbreak in the country linked to a frozen tomato product and the implicated strain had not been detected in Finland before.

Several people reported symptoms following meals in late January 2021 at a restaurant in western Finland, according to the study report published in the journal Eurosurveillance.

The Finnish Institute for Health and Welfare (THL) was informed of 44 outbreak-related patients. THL and the Finnish Food Authority (Ruokavirasto) joined the local outbreak investigation team to help with the epidemiological and microbiological work.

Altogether, 393 meals were sold and 101 people who ate 142 meals participated in the study. Exposure took place in one restaurant over three days.

There were 49 patients; 23 were laboratory-confirmed infections with multidrug-resistant Salmonella Typhimurium. More men than women were affected and patients ranged in age from 16 to 77 years old. Two patients were hospitalized and one had a Salmonella-positive blood culture but there were no deaths. Two asymptomatic staff members were positive for Salmonella.

The outbreak strain was resistant to multiple antibiotics, including fluoroquinolones. 

imported tomato cubes likely source
A local environmental health authority inspected the restaurant in early February 2021. Most food items were bought from one wholesaler. A nearby grocery store was occasionally used for purchases. During the visit, there was ongoing renovation. Meals served in the buffet were cooked in the morning on the day of serving, and they were placed next to each other.

The agency advised the restaurant to intensify cleaning. It was asked to replac fabric towels in the staff bathroom with disposable ones and advised to freeze food samples in the future.

There were no samples of the salads containing frozen tomato cubes left for analysis but tomato cubes from different batches were tested. One of two samples taken from the local wholesaler in February was positive for Salmonella. However, scientists could not trace the origin of the contamination.

Salmonella Typhimurium isolates from patients and frozen tomato cubes used uncooked in two different salads were closely related. These salads were consumed by three-quarters of patients.

Frozen tomato cubes came to Finland via intra-EU trade and the wholesaler was the importer. They were not sold directly to consumers. The wholesaler issued a withdrawal and stopped selling the product until the producer updated the labeling.

No national recommendations for cooking frozen tomato products exist in Finland. Following the outbreak investigation, the producer decided to advise cooking such products before consumption.