But part of the problem is also the food production and distribution system.
Any one beef patty will contain meat from several different animals. "One contaminated animal can screw up a big batch of ground beef," said Dr. Helene Andrews-Polymenis, assistant professor of microbial and molecular pathogenesis at Texas A&M Health Science Center College of Medicine.
And it's not that easy to spot which animals really are sick, because those carrying potentially harmful germs in their intestines don't have any symptoms, Andrews-Polymenis said.
"Obviously sick animals get removed from the slaughterhouse, but these animals aren't sick," she said. "We have to find better ways to figure out what's going on. One of the ways is doing basic microbial testing on carcasses. The more public money spent on research and food-safety issues, the less we're going to have these problems."
Hansen added that supplies of meat used for hamburger patties will often be used from one day to the next. If it's not kept under strict conditions, it's a recipe for growing bacteria.
Then there's the larger issue of the industrialization and centralization of the nation's food system.
"The  spinach recall was Natural Selection foods. They packed spinach for how many different brands? Dozens and dozens," said Hansen. "When you start concentrating things, a little problem can become quite a big one."
Globalization of food production also plays a part. "We're getting products from all over the world more frequently now than ever before," said Tierno, author of
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