Each year, a particularly virulent food-poisoning agent sickens some 73,000 people in the United States, killing about 60. Though scientists have known that beef is the primary route of exposure to this bacterium—an Escherichia coli strain known as O157:H7—most tests had indicated that no more than 2 percent of sampled cattle were infected.
A federal study now suggests that those earlier surveys grossly underestimated the share of animals carrying the fecally transmitted germs. Using more sensitive assays than had traditionally been employed, investigators found that 28 percent of cattle entering large slaughterhouses were contaminated.
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