Rocket salad linked to Swedish Salmonella outbreak
What it found
A large Salmonella Typhimurium outbreak in Sweden in autumn 2022 was linked to pre-washed, pre-packed rocket salad produced in Sweden.
The outbreak involved 109 confirmed cases in Sweden and 20 more cases in other Nordic countries.
What they found
Studies in people
Cases and symptoms
There were 109 confirmed cases, with a median age of 52 years and 62% female. Among 52 cases who answered, diarrhoea, fever and stomach pain were common, and 22 were hospitalised.
Rocket salad link
In a case-control study, cases were more likely to have eaten rocket salad and bagged mixed salad than controls. The link was stronger when both rocket salad and bagged mixed salad were eaten.
International cases
Finland reported 18 cases with closely related isolates, and Denmark and Norway reported one case each. The UK reported seven cases with related isolates, but these were notified 7 to 14 months earlier and were not likely linked to this outbreak.
Other findings
Trace-back to producer
Trace-back showed that bagged rocket salad and mixed salad sold at one grocery retailer came from a single packaging company in Sweden. That company bought rocket salad from three growers in southern Sweden.
No lab confirmation
No microbiological analyses of rocket salad were performed, and no food samples were available for testing. The conclusion was based on epidemiological and trace-back evidence.
What the authors conclude
“Our investigation indicates that, regardless of pre-washing procedures in the production chain, bagged leafy greens such as rocket salad, may contain Salmonella and cause outbreaks, posing a health risk to consumers.”
Also in their conclusions
- They conclude that rocket salad produced in Sweden was the source of this large Salmonella Typhimurium outbreak.
- They emphasise the need for primary producers of leafy greens to identify possible contamination points to prevent outbreaks.
- They state that "bagged leafy greens such as rocket salad, regardless of pre-washing procedures in the production chain, may contain Salmonella and cause outbreaks, posing a health risk to consumers".
How it was done
Salmonella Typhimurium is one of the most common causes of food-borne gut infections in Sweden, and in autumn 2022 an outbreak occurred. The investigation aimed to assess the extent of the outbreak, identify its source and prevent further cases.
They investigated 109 confirmed cases with symptom onset between 17 September and 24 November 2022, reported from 20 of 21 Swedish regions. They ran a case-control study with 54 cases and 434 controls, and did a trace-back investigation with Finnish authorities.
What it can’t tell you
- No microbiological confirmation was obtained from food samples, so the link to rocket salad is based on epidemiological and trace-back evidence.
- The study cannot show how the rocket salad became contaminated, as no samples from irrigation water or fields were tested.
- Recall bias may have affected what cases and controls remembered about what they ate.
Who paid
- Conflicts
- Conflict of interest: None declared.
- Authors work at
- Public Health Agency of Sweden (PHAS), Sweden; European Centre for Disease Prevention and Control (ECDC), Sweden; Swedish Food Agency (SFA), Sweden
The paper
- Title
- Outbreak of Salmonella Typhimurium linked to Swedish pre-washed rocket salad, Sweden, September to November 2022
- Type
- Study
- Evidence
- Studies in people
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Fischerström K, Dryselius R, Lindblad M, et al (2024). Outbreak of Salmonella Typhimurium linked to Swedish pre-washed rocket salad, Sweden, September to November 2022. Euro surveillance. doi:10.2807/1560-7917.ES.2024.29.10.2300299Free full textPubMed 38456218DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error