The outbreak strain was detected in France from a mixed salad dish, containing cherry tomatoes and green leafy vegetables, prepared on 17 August 2022 but not served. Tomatoes from the salad in France and tomatoes in Austria were suspected as the vehicle of infections by national authorities and were traced back to wholesalers in Germany, the Netherlands and Spain, and to growers in the Netherlands, Spain and Morocco. In the absence of microbiological evidence from the tomatoes, the source of the infections could not be established.
The genetic similarity of the human outbreak strains suggests a likely common source(s) causing a prolonged, cross-border foodborne outbreak with cases intermittently reported in 11 EU/EEA countries, the UK, and the US for about 10 months. The contamination may have originated from farms growing tomatoes. Since December 2022, as the number of cases has declined the risk of new infections has decreased to a low level.