The Quang Ngai Department of Health announced on October 17 that tests conducted by the Nha Trang Pasteur Institute had detected Salmonella bacteria in 12 food samples taken from Ba Duoc banh mi shop in Cam Thanh Ward.
The contaminated samples included vegetables, pork sausage, shredded pork, sauces and bread.
E. coli bacteria were also found in three samples, including butter, pork sausage and vegetables.
Salmonella is a common cause of gastrointestinal infections and can be found in contaminated animal products and improperly handled vegetables.
Symptoms typically develop within six to 72 hours of infection and include vomiting, fever and diarrhoea, which can lead to severe dehydration.
The outbreak was first reported on October 9, when 16 people in Quang Ngai were hospitalised with suspected food poisoning. The number subsequently rose to 167.
All affected patients had reportedly eaten banh mi from the Ba Duoc shop, a popular local outlet selling around 350-400 sandwiches daily.
Health officials and police inspected the premises following the outbreak. Initial checks found that the owner had not provided sufficient documentation establishing the origin of ingredients used in the sandwiches.
Authorities ordered the shop to suspend operations and collected food samples for testing to determine the cause of the outbreak.