Food poisoning caused by bacteria such as salmonella kills more people than was previously thought, according to Danish scientists.

Kare Molback and scientists at the Statens Serum Institute in Copenhagen, whose research was reported in the British Medical Journal, believe that deaths from food poisoning could be twice as high as current estimates, with deaths occurring up to a year after infection.

"This has never been studied before because people have always thought of salmonella and campylobacter as acute infections. But what we observe is that for some patients there is a late excess mortality up to one year after infection," Molbak was quoted as saying by Reuters.

For most people, infections from bacteria such as salmonella from poultry products and eggs, and campylobacter from chicken, result in symptoms such as vomiting, diarrhoea and fever, which tend to last only a few days. But for certain at-risk groups, for example the very young, the elderly and those with illnesses such as HIV, food poisoning can be fatal.

The Danish scientists studied the medical history of 1,071 people who had died within a year of being infected with salmonella, campylobacter, Yersinia enterocolitica and Shigella.

Yersinia enterocolitica is bacteria found in pork and Shigella is found mainly on imported fruits and vegetables.

Deaths within the first year after infection were 2.2% in the people who had had food poisoning, compared to 0.7% in a control group of 3,636 people, reported Reuters.