OMAHA, Neb. -- Officials at Nebraska Beef, Ltd., said they may never know why cattle were infected with E. coli or where it came from.

The 160,000 pounds of beef involved in the company's latest recall was processed June 24.

An attorney for Nebraska Beef said the meat was sprayed with lactic acid, which should have killed any bacteria.

Attorney Bill Lamson said the company is confident no illnesses have been associated with the latest recall. Any effects from that meat, he said, should have been apparent by now.

Mike Johanns, the former U.S Agricultural Secretary, said, "I tell you the USDA takes these issues very seriously. It's the top priority. That's why the recall expanded."

The former Nebraska governor said the outbreaks are rare and that Nebraska Beef is safe.

According to the USDA, the best way to protect against E.coli contamination is to cook meat thoroughly to 160 degrees.