Here's how it happens: In the early '90s, farmers in several countries, including the U.S., started feeding animals fluoroquinolones, a family of antibiotics that includes drugs such as ciprofloxacin. In the following years, the once powerful antibiotic Cipro stopped working 80 percent of the time on some of the deadliest human infections it used to wipe out. Twelve years later, the New England Journal of Medicine published a study linking people infected with a Cipro-resistant bacteria to pork they had eaten.
Johns Hopkins University health sciences professor Ellen Silbergeld, who has reviewed every major study on this issue, said there's no doubt drug use in farm animals is a "major driver of antimicrobial resistance worldwide."
"We have data to show it's in wastewaters and it goes to aquaculture and it goes here and there," agreed Dr. Stuart Levy, an expert on antibiotic resistance at Tufts University in Boston. "Antibiotic use in animals impacts everything."
Farmer Craig Rowles remains unconvinced.
It's afternoon in one of his many rural Iowa pig barns, roaring with snorting and squealing pigs. Some snooze in corners, while others hustle toward their troughs, their slop laced with a steady supply of antibiotics.
"If there was some sort of crossover between the use of the antibiotics in animals and the antibiotics in humans, if there was in fact a real issue there, wouldn't you think we would have seen it?" said Rowles, also a veterinarian who sells 150,000 hogs a year. "That's what the science says to me."
The modular modern barn, home to 1,000 pigs, is a hygienic place. Manure plops through slatted floorboards; an invisible funk steams back up. Rowles dons a sanitary white paper jumpsuit and slips plastic booties over his shoes; he's anxious that his 100-pound pigs aren't exposed to outside germs. A few sick swine are isolated, corralled in a pen near the entrance.
Antibiotics are a crucial part of Rowles' business, speeding growth and warding off disease.
"Now the public doesn't see that," he said. "They're only concerned about resistance, and they don't care about economics because, 'As long as I can buy a pork chop for a buck 69 a pound, I really don't care.' But we live in a world where you have to consider economics in the decision-making process of what we do."
Rowles gives his pigs virginiamycin, which has been used in livestock for decades and is not absorbed by the gut. He withdraws the drug three weeks before his hogs are sent for slaughter. He also monitors his herd for signs of drug resistance to ensure they are getting the most effective doses.
"The one thing that the American public wants to know is: Is the product that I'm getting, is it safe to eat?" said Rowles, whose home freezer is full of his pork. "I'm telling you that the product that we produce today is the safest, most wholesome product that you could possibly get."
Some U.S. lawmakers are fighting for a new law that would ban farmers like Rowles from feeding antibiotics to their animals unless they are sick.
"If you mixed an antibiotic in your child's cereal, people would think you're crazy," said Rep. Louise M. Slaughter, D-N.Y.
Renewed pressure is on from Capitol Hill from Slaughter's bill and new rules discussed in regulatory agencies. There is also pressure from trade issues: The European Union and other developed countries have adopted strong limits against antibiotics. Russia recently banned pork imports from two U.S. plants after detecting levels of tetracycline that the USDA said met American standards.
Farmers and drugmakers are battling back. Pharmaceutical companies have spent $135 million lobbying so far this year, and agribusiness companies another $70 million, on a handful of issues including fighting the proposed new limits. Opponents, many from farm states, say Slaughter's law is misguided.