An infected knife may have been the source of E. coli contamination that resulted in a massive beef recall last summer. The head of Colorado State University's meat-science center says a knife at the Swift and Company plant in Greeley was likely contaminated with fecal matter while removing a hide. Gary Smith says the knife then inadvertently sliced into meat. None of the multiple food-safety steps used on the carcass after the skinning would have killed pathogens within the meat. Twenty-two people who ate beef traced to the Greeley plant reported diarrhea and vomiting last year. That prompted the recall of 18-point-six million pounds of ground beef. Smith says other contamination sources are possible. He says meat scraps and fat used to make ground beef are handled up to 30 times before becoming a hamburger.