E. coli infections from strain 0157:H7 have been blamed for sickening 70,000 people every year. Recently, two outbreaks in New York and Massachusetts took two lives and sickened dozens more, including 11-year-old Austin Richmond.
"I've never seen anything come on so strong," said Austin's mother, Jaimee Richmond. "He was fine when he came home and by 4 o'clock in the morning, he was having stomach cramps, [was] nauseous, vomiting."
Austin's sickness was traced to a cheeseburger he ate at a school camp. According to experts, infected hamburger meat is a leading cause of E. coli-related sickness.
A "Good Morning America" investigation found that what is generally thought to be a simple meal -- the classic American burger -- can be much more complex.
For its investigation, "Good Morning America" purchased six packages of 100 percent ground beef patties from major supermarket chains in Seattle and took the patties to IEH Laboratories, one of the meat industry's largest independent testing labs.
"We isolate DNA from each," said Mansour Samadpour of IEH. "We looked at eight pieces of meat from each hamburger patty."
When the results came back, the lab reported at least four cows had been found in each patty -- and sometimes as many as eight.
"Unfortunately, I don't think customers realize what goes into a single hamburger," Sarah Klein of the Center for Public Interest told "GMA." "I think we have a fantasy it's still coming from a single cow."
According to American Meat Institute President J. Patrick Boyle, there is a reason that beef from multiple cows winds up in a single hamburger.
"Our ground beef supply is a combination of different types of meat in proportion to certain levels of fat," Boyle said. "So one has to have multiple sources of the raw material to make the finished product that Americans enjoy so much."
But it's the multiple sources that can also make your hamburger vulnerable to bacteria like E. coli, since a single infected cow could be mixed into lots of ground beef.
Slaughterhouses are federally required to test their meat for E. coli and meat processors also have to have a safety plan, which often includes testing of the ground beef, although that is not required.
"What we require is that the product is safe," said Elisabeth Hagen, chief medical officer of the U.S. Department of Agriculture. "A lot of companies will utilize finished product testing in order to help ensure that. Other companies will utilize testing of the incoming source material."
Some critics say that's not enough, and they are pushing for tougher federal standards for testing ground beef.
"We need to see as much testing as possible all the way along the production chain so we can catch a problem early on," Klein said. "Right now, that's just not being done."
According to Hagen, testing would not guarantee safety.
"You know testing alone does not ensure safety of a product. It's important to look all the way back through the entire continuum," Hagen said. "The product needs to be made safely and testing at the end product provides some additional assurances, but it's not the only thing that is going to guarantee the safety of a product."
The USDA has inspectors at every meat facility, but critics complain the agency conducts only 15,000 spot tests a year for E. coli.