70 percent of the antibiotics used in this country -- 70 percent! -- go into livestock production. And that's before you even get to the antibiotics that are used on animals who actually fall ill.
The reason is simple enough: If we didn't pump our livestock full of antibiotics, they would get sick. They are, after all, packed into dim and dirty enclosures. They're stacked on top of one another. And they're being fed food they didn't evolve to eat. All of this makes animals sick. But rather than raise them in a way that doesn't make them sick, but costs somewhat more, we just keep them on constant doses of antibiotics.
And then we eat them. Which means we get constant, low-grade doses of these antibiotics. Which means common bacteria get constant, low-grade doses of these antibiotics. And there's mounting evidence that this background exposure to antibiotics is contributing to the startling rise in antibiotic-resistant bacteria.
Everything from staph to strep to salmonella is exhibiting uncommon resilience in the face of our latest drugs. A 2003 World Health Organization study (PDF) put it pretty starkly: "There is clear evidence of the human health consequences [from agricultural use of antibiotics, including] infections that would not have otherwise occurred, increased frequency of treatment failures (in some cases death) and increased severity of infections." Even stronger was the title of a 2001 New England Journal of Medicine editorial: "Antimicrobial Use in Animal Feed -- Time to Stop."