Contaminated lamb meat caused a Salmonella outbreak in a minority ethnic community in Wales, according to researchers.

In July 2021, Public Health Wales received two notifications of Salmonella. Both patients had attended a barbecue in a park in Cardiff to celebrate Eid al–Adha, two days earlier. Other cases related to the barbecue were found and an outbreak investigation was started.

The barbecue was attended by members of the North African community. On the same day, smaller lunches were held in three homes. Many people went to both a lunch and the barbecue.

A traditional raw liver dish called marara, served at the barbecue, was the likely vehicle for infection. Marara is made from raw liver, usually cut into strips, washed in lemon juice and vinegar, and marinated in herbs, spices, and peanut butter. Meat and offal came from two local butchers with the same supplier and samples had identical whole genome sequences as cases.

In total, 22 cases were identified in the outbreak, of which five were confirmed and 17 were probable Salmonella Typhimurium cases, according to the study published in the journal Epidemiology and Infection.  

Cross contamination factor

Five people developed symptoms in the eight days following the barbecue, which suggests person-to-person transmission since some of them had attended the barbecue but did not become unwell until after the incubation period for salmonellosis.

Many cases were severely unwell, with 12 seeking emergency hospital care and six being admitted overnight. One patient needed treatment in an intensive care unit.

One respondent noted gastrointestinal sickness in a barbecue attendee and resident in their household, with symptoms starting before the barbecue. The barbecue food was prepared at home by eight people. It was transported, not chilled, to consume at the evening barbecue, and included marinated uncooked lamb, several side dishes, and a number of traditional dishes.

The religious practice involving animal slaughter for Eid al-Adha is called Qurbani. The day of the barbecue was very hot, plus the raw liver and lamb was left unchilled for a long period.

Questionnaire responses indicated that some lamb cooked on the barbecue was pink inside and that marinade from the raw liver was used as a dip for other food. One person used the plate the raw liver was served on to eat their meal. All of this offers multiple opportunities for cross-contamination, said scientists.

Sequences from 11 samples of leftover raw lamb were genetically indistinguishable from one another, and from those in the five human isolates from barbecue attendees.

Three people had more than one pathogen in their stool sample including two co-infections with Shiga toxin-producing E. coli (STEC) and one with Campylobacter. Identical E. coli sequences to those in patients were found from samples taken from the butchers and supplying abattoir.

Wider ongoing outbreak

Microbiological evidence suggests there was widespread contamination of sheep meat consumed at the barbecue, and that cross-contamination with other dishes occurred. However, it was not possible to establish wher contamination occurred in the food chain.

The five sequenced cases are part of a larger ongoing cluster with cases since 2018. They are spread across Wales, Scotland, London, and the South West and Midlands of England. At least two cases in the wider cluster were people with occupational contact with sheep farms, suggesting a possible transmission chain with a farm origin. Investigations are ongoing to find the source.

An educational session was held during the Eid al-Adha festival which included members of the community that eat the traditional marara dish and others that celebrate Eid al-Adha. Key food safety and hygiene messages were presented followed by a conversation. The session received positive feedback from participants. A communication campaign, noting different cultural practices, was developed with the affected community.

“Future outbreak investigations should be relevant to the community affected by considering dishes beyond those found in routine questionnaires,” said scientists.