The likely source of contamination in a Salmonella outbreak that has sickened more than 50 people is related to handling raw egg products, according to Australian authorities.

An investigation into the outbreak associated with three Angkor Bakery stores found a number of food and environmental samples collected from stores last week were positive for Salmonella.

In an updat from the initial announcement of 11 cases and nine hospitalizations one week ago, South Australia (SA) Health reported 51 people ill. Nineteen of the patients had to be admitted to hospitals.

Cases were reported to the agency among people who had eaten Vietnamese rolls from the three bakeries. The sites closed during the investigation but have now reopened. Stores at Springbank Plaza in Burton, Hollywood Plaza in Salisbury Downs and Blakes Crossing Blakeview were affected.

Dr. Fay Jenkins, SA Health’s acting director of public health services, said given the sample results and strain of the Salmonella outbreak it was likely the cause of contamination was related to handling raw egg products.

“The owners of the Angkor Bakery stores continue to work closely with the local councils and SA Health to improve their practices, and all three bakeries closed voluntarily during the investigation. Following the remediation work, subsequent tests returned negative results for Salmonella, and all three of the businesses are able to reopen. They will be closely monitored by the local council.”

SA Health officials said raw egg products can be risky ingredients if not appropriately handled, and safe handling practices should be followed by businesses and in the home.

Jenkins said many food poisoning outbreaks have been associated with foods containing raw or partially cooked eggs such as aioli, mayonnaise, hollandaise or tartare sauce and mousse.

“The external shell of eggs may contain harmful bacteria such as Salmonella, and while eggs may not necessarily look or smell off they may be contaminated. It’s important to check that eggs are clean and not cracked or dirty – and those that are should be thrown out,” she said.

“Preparation surfaces and utensils should be thoroughly washed, sanitized and dried after handling eggs, and remember to think of raw eggs like raw meat, and wash your hands thoroughly after handling them.”

People can experience symptoms of Salmonella infection between six and 72 hours after exposure and these usually last for three to seven days. They include fever, diarrhoea, vomiting, headaches, stomach cramps and loss of appetite. More severe symptoms may occur in young children, older people, pregnant women and people who are immunocompromised.