Chris Waldrop, director of the Consumer Federation of America’s Food Policy Institute in Washington, D.C. sees a disturbing return:

"It looked like (improvements in food safety) were working, but something has happened. Something’s going on in the food supply chain. We need to figure out what that is. We can’t let our guard down. We need to have the same level of vigilance."

Testing at beef processing plants varies from processor to processor, but relies on a combination of industry and USDA guidelines and beef industry "best practices," according to the Sacramento Bee.

In a 2006 Texas A&M study prepared for the beef industry, examples included sampling finished ground beef products every 15 minutes to test specifically for E. coli O157:H7; documenting the source of raw material through lot or serial numbers; and discouraging the introduction of excess meat into the processing flow.

The United Foods recall is the largest of a number of recalls in recent months. In all, more than 6 million pounds of ground beef and related products have been recalled from stores and distribution sites in 25 states since April.