Last week, federal officials announced recalls of ground beef and organic walnuts because they were potentially contaminated with E. coli bacteria that can make people sick. The recalls involve more than 16,000 pounds of ground beef distributed by Cargill Meat Solutions and sold at Wal-Mart stores in 11 states, as well as organic shelled walnuts sold in bulk in natural food and co-op stores in 19 states. So far, the recalled walnuts have been associated with 12 illnesses, including seven...