That declaration makes Tyson the latest in a line of major food processors getting out of antibiotic use, including McDonald's, Perdue, and Chick-fil-A.

In a way, that's all good news, especially for the interest groups that have been pushing for more than a decade to cut antibiotic use in food animals. But their nominal goal—to quell the rising tide of drug-resistant human pathogens that cause an estimated 2 million infections and 23,000 annual deaths in the US each year—isn't as simple as denying amoxicillin to McNuggets. Because scientists don't actually know everything they need to about how and how often antibiotic-resistant bacteria move from livestock to people. And until they get a better handle on the conditions that allow resistant genes to flourish, turning animal pathogens into human ones, they won't be able to determine the best way to combat them.