Rapid Outbreak Assessment by ECDC/EFSA on the Persistent Outbreak of Salmonella Strathcona ST2559 Linked to Cherry Tomato Consumption Across Multiple Countries in the EU/EEA and the United Kingdom

On 12 November 2024, the ECDC and EFSA jointly published a Rapid Outbreak Assessment (ROA) on the cross-border outbreak of Salmonella strathcona ST2559, affecting 16 countries within the European Union (EU), the European Economic Area (EEA), and the United Kingdom (UK).

The ROA provides an overview of the epidemiological situation, the results of sample analyses conducted in each country, the ongoing control measures, and recommendations for future actions.

Between 1^st January 2023 and 5November 2024, 232 confirmed cases (as for the EU case definition) of S. strathcona ST2559 have been identified in the following EU/EEA countries: Austria (33), Croatia (3), Czech Republic (10), Denmark (9), Estonia (1), Germany (62), Finland (3), France (23), Ireland (1), Italy (67), Luxembourg (2), Netherlands (2), Norway (3), Slovakia (5), Slovenia (2), and Sweden (6). In the UK, 29 cases have been reported. Among travel-associated cases, Italy emerged as the most frequently visited country.

Epidemiological investigations conducted in various countries in response to the outbreak identified cherry tomatoes as the vehicle of infection. Specifically, investigations into outbreaks in Austria (2023) and Italy (2024) confirmed that cherry tomatoes from the Sicily region in Italy were the source of infection in both instances. This conclusion aligns with findings from an earlier outbreak of S. strathcona ST2559 in Denmark in 2011.

Whole-genome sequencing and subsequent cluster analyses suggest a recent common origin of the epidemic strain, which has affected multiple nations.

In Italy, outbreaks were reported between late September and early October 2024 in Tuscany and Umbria regions, with over 300 symptomatic cases linked to primary schools and childcare facilities. Thus far, 46 of these cases have been confirmed as S. strathcona, and the food isolate identified in Tuscany was part of the S. strathcona ST2559 cluster. Sequencing of nine clinical isolates from the Umbrian outbreak also confirmed the presence of S. strathcona ST2559. Microbiological analyses of clinical samples are ongoing.

Health and food sector investigations are continuing to determine whether cherry tomatoes from Sicily are the source of infection across all EU countries reporting cases, as other foods could also be involved in the transmission. Consequently, the Italian Ministry of Health has deemed it necessary to implement a sampling and testing plan to detect Salmonella strathcona in cherry tomatoes (both “ciliegino” and “datterino” varieties) sold in Italy. The plan requires each Local Health Authority (ASL) to perform at least one sampling by 31 December 2024. Test results will be submitted to the Ministry of health through the RaDISAN information system.

Furthermore, the role of environmental factors in tomato contamination requires further investigation, as the strain has also been identified in an animal raised in the Sicily region. Additional ROA recommendations include tracing the entry point of S. strathcona (for example, through irrigation water) to implement corrective measures, halt its spread, and prevent future cases.

Source: EFSA