Alison Young of USA Today reports today U.S. Department of Agriculture staff regularly on site at two Iowa egg processors implicated in a national salmonella outbreak were supposed to enforce rules against the presence of disease-spreading rodents and other vermin, federal regulations show.

Doug Powell, an associate professor of food safety at Kansas State University, said regulations are only as good as their enforcement, adding, "It goes back to the responsibility of whoever is producing the food. How do you establish a corporate culture where people pay attention to food safety?"

The USDA egg graders, part of an industry-paid program, were at Wright County Egg and Hillandale Farms at least 40 hours a week — including before the outbreak — inspecting the size and quality of eggs inside processing buildings.

Though USDA regulations say buildings and "outside premises" must be free of conditions that harbor vermin, the agency takes a narrow view of its responsibilities. Under the USDA’s unwritten interpretation of the regulations, egg graders only look for vermin inside the specific processing building where they are based, said Dean Kastner, an assistant USDA branch chief in poultry grading program.

The agency interprets outside premises as only the area immediately around the processing building’s loading dock and trash receptacle, he said.

Salmonella can be spread by rodents and wild birds. Outbreak investigators from the Food and Drug Administration (FDA) this week released reports documenting filthy conditions in and around egg laying barns at the two companies, including rodents, rodent holes, wild birds, flies and other vermin.

Hillandale Farms spokeswoman Julie DeYoung said the barns at its facility are about 50 feet from the processing building. At Wright County Egg, the laying barns are 50 feet apart and connected to the processing plant, said spokeswoman Hinda Mitchell.

Associated Press subsequently reported two former workers at Wright County Egg facilities, Robert and Deanna Arnold, say they reported problems such as leaking manure and dead chickens to USDA employees but were ignored and told to return to work.

The salmonella outbreak has led to a recall of about 550 million eggs.