New York, June 8 (IANS) Salmonella poses the greatest health threat to America, the US Center for Disease Control and Prevention said.

Salmonella infection has risen 10 percent over the past 15 years, while several types of food-borne illness have been falling, Xinhua reported citing an agency statement.

Infection from E. coli O157 - the strain of most concern in the US - has dropped almost by half and the rates of six other food-borne infections have gone down by 23 percent, the centre said.

"There are about 50 million people each year who become sick from food in the US. That's about one in six Americans," centre director Thomas R. Frieden said.

The centre attributed the reduction in infection from E. coli O157 to better detection and investigation of outbreaks, cleaner slaughterhouse methods, better testing of ground beef and improved inspection of beef processing plants.

Other food-borne illnesses that fell in incidence over the same period include those caused by the campylobacter, listeria, vibrio and yersinia pathogens.

Salmonella infection in humans is usually contracted from sources like poultry, pork, beef, eggs and milk when not prepared, handled, or refrigerated properly.

Most people infected with Salmonella develop diarrhoea, fever, vomiting, and abdominal cramps. In severe cases, the infection may spread from the intestines to the blood stream, and can cause death unless the person is treated promptly with antibiotics.