Most children are sick during an outbreak of Salmonella eggs in China

A Salmonella outbreak that has primarily sickened children in China was caused by contaminated kitchen mayonnaise used in egg sandwiches, a study has found.

In September 2019, the Centers for Disease Control and Prevention in Shenzhen and Dongguan were notified of a large cluster of suspected gastroenteritis mainly involving children who visited hospitals in the two cities.

A total of 254 cases have been reported in Shenzhen and Dongguan, Guangdong province, the study published in the journal found. Frontiers in microbiology.

Demographic data and exposure questionnaires were obtained for 121 patients. The age range of those ill was 2 to 61 with most young children but a few teaching staff and a few family members of staff consuming leftovers taken home.

Most people had fever, diarrhea, abdominal pain and vomiting. A person with severe diarrhea, vomiting and fever was admitted to the intensive care unit, but no one died. The distribution of cases over three days suggests a point outbreak with a single incubation period.

Children in half-day courses were picked up at noon and did not receive lunch or snacks in the afternoon. The researchers said that snack in the nursery canteen on September 20 may have led to the outbreak.

Epidemiological evidence indicated that all the patients had consumed egg sandwiches served as snacks for children and staff at a nursery in Dongguan, located near Shenzhen.

Interviews revealed that mayonnaise containing raw eggs was spread directly on bread, made into sandwiches and served without heating.

Test results and traceability
During the investigation period, the nursery was suspended; pending a review of food preparation procedures in the canteen.

Salmonella Enteritidis has been isolated from case-patients, food handlers, kitchen utensils, and sandwiches with kitchen-made mayonnaise.

Of 113 samples, 66 were positive for Salmonella Enteritidis, mostly from patients but also from food samples, food handlers and the mayonnaise mixing bowl.

The researchers said the outbreak highlights the importance of basic kitchen hygiene and the food safety challenges posed by using raw egg ingredients, especially in a nursery.

“This can be achieved by strengthening food safety training and supervision for food service providers and/or caterers in nurseries, such as the use of pasteurized egg products or avoiding recipes using raw eggs, which must be fully cooked. Hygiene measures included washing hands and using gloves before handling food, while raw and cooked foods are processed and stored separately to avoid cross-contamination.

A traceback investigation confirmed that the eggs used for the production of mayonnaise during the outbreak were purchased from the market in Dalingshan, Dongguan and sourced from an egg distributor in Anshan, Liaoning province, from a farm of Hebei chickens.

Due to a lack of cooperation from the egg producer, distributors and wholesalers, the team was unable to obtain samples or isolates and therefore could not establish a pathway for final transmission in the supply chain.

The scientists said the lack of data sharing and communication channels is a common problem with foodborne investigations and surveillance in China.

They added that the overall results highlight the benefits of supplementing traditional epidemiological investigations with whole genome sequencing analysis to present definitive genomic evidence linking suspected food sources to infections.

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