The number of samples of ready-to-eat meat and poultry products that were found to be contaminated with listeria bacteria fell by 25% in the first nine months of this year, according to the US Department of Agriculture.

Of the 7,500 meat samples tested by the USDA's Food Safety and Inspection Service (FSIS) in the first nine months of this year, 0.75% tested positive for the bacteria, compared to 1.03% for the whole of last year, reported Reuters.

"FSIS has taken aggressive action to prevent contamination of ready-to-eat meat and poultry products by listeria monocytogenes and our testing is verifying that our programs are effective," FSIS Administrator Garry McKee was quoted by Reuters as saying.

The FSIS has stepped up tests and inspections of meat plants after meat companies recalled a record amount of meat last year.

Listeria, which is destroyed when a product is heated to at least 71C, can cause fever, headaches and nausea, and can be very serious in those with weak immune systems.