A Salmonella outbreak in England that sickened more than 60 people earlier this year has been linked to eggs from Poland.

Samples from patients are also similar to previously reported isolates that fall into a cluster that is part of several national and international investigations.

There were 65 cases associated with the English outbreak; 25 confirmed and 18 probable infections linked to a restaurant, ten confirmed with unknown links to the establishment, and 12 with no link to the restaurant. 

The outbreak linked to the unnamed restaurant was reported to the UK Health Security Agency (UKHSA) East of England Health Protection Team in early April. UKHSA was notified of multiple cases of gastroenteritis following food consumption at the site, with attendance or takeaway dates in late March, according to a study published in the journal Eurosurveillance.  

Ten people hospitalized
Whole genome sequencing (WGS) results indicated Salmonella Enteritidis infection. Researchers identified additional patients with no known links to the restaurant, and historical cases reported since July 2022.

based on completed questionnaires, onset dates ranged from March 17 to April 17, 2023, but most people experienced symptoms on March 30. They included vomiting, diarrhea, fever and abdominal pain 12 to 24 hours after eating at the restaurant. Ten people were hospitalized.

For the 43 restaurant-linked cases, the mean age was 32 with a range of 6 to 61 and 17 were female. There were no cases reported among staff.

Epidemiological investigations suggested eggs or chicken as the likely cause of the outbreak. Due to an overlap in menu items, it was not possible to separate consumption of the two items. Eating chicken or egg would explain, respectively, 25 or 24 of 31 cases. 

When environmental health officers visited the restaurant in early April, there were no remaining food items to sample. They identified no lapses in food safety or hygiene concerns such as cross-contamination issues or inadequate cooking of chicken.

Raw eggs were used to make garlic mayonnaise and as a binder ingredient in naan bread. General advice to the business included a recommendation to change supply to domestically sourced eggs produced under a recognized farm assurance scheme.

Eggs from Poland suspected
Investigations by the Food Standards Agency (FSA) found that eggs used at the restaurant were purchased from wholesalers who had imported them from Poland. Two cases with no link to the restaurant also consumed eggs from Poland. Information on the source of the chicken is pending.

The narrow window of dining dates for restaurant-linked cases suggests a contaminated food batch or an isolated lapse in procedures, said researchers.

It is possible that chicken and eggs are independently associated with illness: either through cross-contamination at the restaurant, or due to potential widespread contamination within multiple chicken sectors. While chicken cannot yet be ruled out as the source, findings so far suggest eggs were the main vehicle of the restaurant outbreak, found the study.

Since 2014, Europe has seen related illnesses associated with chicken meat or eggs from multiple origins across Europe.

Data was shared on the EpiPulse platform, hosted by the European Centre for Disease Prevention and Control (ECDC). Information from Austria and Poland indicates closely genetically related cases in these countries.