At least 24 cases of listeria bacteria infection have been detected in Denmark, health authorities said Monday.

According to the State Serum Institute (SSI), the number includes four more Danish people, who were confirmed to have been infected with listeria, Xinhua reported.

A Hedehusene-based sausage company has proved to be the main source of the infection, the institute said.

Although the company is closed and all suspected products have been recalled. SSI expects that more cases may continue to pop up in the coming weeks as it typically takes several weeks for symptoms to surface.

A total of 12 people have been believed to be died as a result of the listeria outbreak so far.

Some 30 products, including variations of cold cut sausages, salami and hot dogs have been withdrawn from the market.

Regulatory control over listeria is now tightened, ministry of food, agriculture and fisheries said.

Listeria is a bacteria found in soil, water and in the intestines of some animals.

The bacteria can also live in food processing plants and unlike other germs, it can survive refrigeration.

Symptoms of listeria include weakness, vomiting, diarrhoea and fever.