Threats and outbreaks of salmonellosis

Latest outbreak

Multi-country outbreak of Salmonella Mbandaka ST413 linked to ready-to-eat chicken meat

(update as of 21 March 2024)

A cross-border outbreak of Salmonella Mbandaka ST413 has been ongoing in the European Union/European Economic Area (EU/EEA) and the United Kingdom (UK) for over two years since September 2021. By 30 November 2022, 196 cases had been recorded and published in a joint European Centre for Disease Prevention and Control (ECDC) and European Food Safety Authority (EFSA) Rapid Outbreak Assessment. By 15 March 2024, 300 cases (an increase of 104 cases) had been reported in Estonia (n=3), Finland (n=98), France (n=16), Germany (n=2), Ireland (n=7), the Netherlands (n=1), and the United Kingdom (n=173), according to the European case definition (Table1). Twenty-three cases were hospitalised, six cases had septicaemia and one case died in the UK.

In November 2022, when the first assessment was published, ready-to-eat chicken products and/or fresh chicken meat were identified as probable vehicles of infection based on case interviews in Finland and the UK. Subsequent investigations by the food safety authorities in Estonia, Finland and the Netherlands and the sharing of genomic food information with EFSA in 2024 identified frozen steam-cooked chicken breast, produced in Ukraine, as the vehicle of infections. The contaminated batches had been imported by non-EU operators and distributed in the EU/EEA and UK markets. Centralised analysis of human and food sequences in ECDC and EFSA One Health whole genome sequencing (WGS) system illustrated the genetic closeness of isolates (Figure 1).

The shelf lives of contaminated frozen chicken meat products expired in November and December 2023. The most recent cases were detected in Finland in October 2023 and in the UK in February 2024. Assuming that the identified contaminated batches are no longer on the market, and given the expiration dates and control measures implemented, the likelihood of new infections occurring with the outbreak strain from these batches is low. However, despite the implementation of control measures, cases continued to occur throughout 2023 in the EU/EEA and in early 2024 in the UK, suggesting undetected routes of exposure which require further investigation and pose a continued, albeit reduced, risk for new infections.

Table 1. Table 1. Number of S. Mbandaka ST413 outbreak cases in six EU/EEA countries and the UK, as of 15 March 2024

Figure 1. Single linkage cluster tree of 100 human and four S. Mbandaka ST413 outbreak isolates, as of 15 March 2024

Source: ROA S Mbandaka chicken update 2024 (microreact.org)

Background information

Various animals (especially poultry, pigs, cattle, and reptiles) can be reservoirs for Salmonella, and humans generally become infected (and develop salmonellosis) by eating poorly cooked, contaminated food or by eating food that has been contaminated by uncooked meat and poultry. The incubation period is 12-36 hours and the severity of illness depends on the number of bacteria ingested, the immune status of the person, and the type of Salmonella. The clinical picture of salmonellosis is characterised by fever, diarrhoea, abdominal pain, nausea and vomiting but can sometimes lead to blood stream infection, and a more severe, systemic form of the disease. Symptoms usually last for a few days and most infections are self-limiting. Children, the elderly and persons with chronic diseases are most vulnerable for severe infections and because of dehydration or invasive infections, hospital admission may sometimes be required. Deaths due to Salmonella infection are uncommon but can occur in young babies and infants, older people, and individuals with weakened immune systems.