Around 60% of the largest US meat plants did not meet federal food safety regulations for preventing E. coli bacteria from contaminating their products, according to the US Department of Agriculture.

In September, the USDA ordered all US beef slaughter and grinding plants to re-examine their food safety programmes after inspectors found that E. coli was more prevalent in meat than was previously thought. USDA officials said that a preliminary review of these examinations found that 60% of 35 large meat plants did not meet federal food safety regulations.

The USDA said consumers should not be alarmed by the findings. "They were scientific and design issues and not direct food safety issues," Garry McKee, administrator for USDA's Food Safety and Inspection Service, was quoted as saying by Reuters.

McKee said that meat plants had been given 30 days to resolve the problem.