"We pulled everything that we have spinach in," said Dan Brettelle, manager of a Piggly Wiggly store in Columbia, S.C.

Consumer activist Barb Kowalcyk said fixing the nation's "fractured network" of food safety agencies could save lives. In 2001, her 2-year-old son, Kevin, died of E. coli, possibly after eating tainted ground beef.

"How can we improve communication between agencies? That needs to happen," the Loveland, Ohio, resident said.

Not all strains of E. coli cause illness: E. coli O157:H7, the strain involved in the current outbreak, was first recognized as a cause of illness in 1982. That strain causes an estimated 73,000 cases of infection, including 61 deaths, each year in the United States, according to the CDC.

When ingested, the bug can cause diarrhea, often with bloody stools. Most healthy adults can recover completely within a week, although some people — including the very young and old — can develop a form of kidney failure that often leads to death.

Sources of the bacterium include uncooked produce, raw milk, unpasteurized juice, contaminated water and meat, especially undercooked or raw hamburger.

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Contributing: Jordan Robertson.