The Codex Alimentarius Commission, an international food safety group, set new guidelines for bagged salads and raw oysters and tightened limits on the amount of melamine in food and infant formula, the World Health Organization said.

The new Codex measures provide specific guidelines for production, harvesting, packing, processing, storage and distribution of leafy green vegetables to prevent contamination by salmonella, E. coli and hepatitis A. The guidelines cover irrigation waters, cooling and storage and correct washing of hands by consumers, the WHO said.

"In relation to salads, fresh salads, the issue is often that you can have contamination because you can have contaminated water that you put onto the fields," Jorgen Schlundt, WHO director of food safety and zoonoses, told Voice of America. "It can be contaminated with everything from human feces to other types of contamination including animal feces. So, the issue is to make sure at the farm that you are doing the right thing. And, these guidelines are defining how you should do this type of production in a hygienic way."

The Codex guidelines also define how to monitor the way oysters are harvested and kept before being consumed. The guidelines state how to safely prepare and produce foods to prevent foodborne disease such as Vibrio.

Codex set a new limit for melamine of 1 milligram per 1 kilogram of powdered infant formula and 2.5 milligrams per 1 kilogram of other food. Melamine was added to infant formula and other milk products in China in 2008, killing six infants and sickening nearly 300,000 others.

Codex is run jointly by WHO and the Food and Agriculture Organization.