A large foodborne outbreak of Salmonella Typhimurium linked to bánh mì, Western Australia, 2024

Abstract

In March 2024, the Department of Health in Western Australia investigated an outbreak of Salmonella linked to a food venue serving bánh mì (Vietnamese sandwiches). Outbreak cases were notified via laboratories, health services, local government, and cases referring sick co-exposed individuals. Structured interviews were conducted to determine demographic, illness and food exposure histories, and descriptive analyses were performed. The investigation identified 146 outbreak cases linked to the food venue. All outbreak cases had symptoms of salmonellosis, and 34 cases (24%) were hospitalised. Descriptive analysis found a strong association between illness and the consumption of bánh mì (139 cases) or tofu salad (three cases) from the food venue. This finding was supported by environmental and laboratory evidence, with Salmonella Typhimurium multilocus variable-number tandem repeat analysis linking 112 cases (77%) to samples from the food venue’s benchtop blender and tofu mix. The contaminated blender had been used to make three products: chicken and pork liver pâté, raw-egg mayonnaise, and a crispy rice tofu. The liver was undercooked before blending and was suspected to be the most likely source of the outbreak. To control the outbreak, the venue stopped using the blender and switched to using commercial mayonnaise, and staff were trained on safer cooking and hygiene processes. The outbreak highlights the critical importance of application of food safety standards in commercial kitchens, especially in relation to commonly used appliances, and to raw liver and mayonnaise products. Furthermore, it demonstrated that open and timely communication between food businesses, local government, laboratories and health agencies are key to the rapid identification of, and response to, foodborne outbreaks.