Two million Americans suffer from antibiotic-resistant infections each year and at least 23,000 people die, according to the Centers for Disease Control and Prevention — and much of the problem may stem from what we eat.
The livestock industry pumps massive quantities of antibiotics into farm animals in order to kill potentially sickening bacteria and boost animal growth. But with each dose, a new opportunity emerges for hardier bacteria to develop and jump from animals to human via farm workers or through the food supply.
It's a problem that could grow exponentially, as developing nations, such as China and India, become wealthier and their populations turn to more protein-rich diets.
Antimicrobial use in livestock production could increase 67 percent worldwide by 2030, according to projections published in the Proceedings of the National Academy of Sciences, and public health advocates worry that the world may be on the precipice of a great health care dilemma.
"Health organizations have said it's one of the crises of the century," Gail Hansen, a public health veterinarian with The Pew Charitable Trusts antibiotic resistance project, told VICE News.
The study is the first to estimate the scale of antimicrobial use in livestock around the world. The researchers estimate that cattle, chickens, and pigs consumed 63,151 tons of antibiotics in 2010.
That's an important baseline because meat eating around the world is growing at an unprecedented rate. And if antibiotic use spikes, too, resistant bacteria may follow.
"We're undergoing this massive change and we need to pay attention to the fact that this is causing people to become sick and die from massive infections," Ramanan Laxminarayan, lead author on the study and a researcher at the Princeton Environmental Institute, told VICE News. "I think that link needs to be stronger in people's minds."
In Asia, for example, animal protein consumption grew from seven grams a day per person in 1960 to 25 grams in 2013. Low to middle-income countries are adopting industrial agriculture methods as they try to fulfill rising demand for meat. That includes using antibiotics to promote growth in healthy animals and to reduce disease risk when hundreds of animals are packed into confined spaces. If factory farms continue those practices, antibiotic use may double in Brazil, Russia, India, China, and South Africa, the study found.
The study assumes that techniques for growing mass quantities of animal protein will remain the same for the next 20 years. That could mean especially grave consequences in the developing world, where people are already at increased risk for bacterial diseases. The researchers note that in India 95 percent of adults already carry bacteria resistant to common antimicrobials, including penicillin.
The World Health Organization warned last year that we're heading for a "post-antibiotic" era, when the drugs that have helped to curb infections in humans no longer have any impact. Bans on antibiotics in livestock feed, however, have helped to staunch the proliferation of antibiotic-resistant diseases.
In 2006, the European Union banned growth-promoting antibiotics in livestock feed. Mexico, Australia, and New Zealand have also limited their application.
Earlier this year, in a study for the Organization for Economic Co-operation and Development, Laxminarayan found that limiting the use of antibiotics in livestock resulted in only small economic consequences.
"I have to say that the EU has shown remarkable leadership in the use of antibiotics," Laxminarayan told VICE News. "They have clearly demonstrated that is possible to do without antibiotics in livestock. It's been disheartening that it hasn't happened in the US as well."
In the United States, livestock accounts for 80 percent of total antibiotic consumption, according to the Food and Drug Administration. In 2013, the agency released voluntary rules to encourage more judicious antibiotic use. They tightened over-the-counter access to livestock antibiotics and banned the practice of feeding healthy animals growth-promoting antibiotics.
Still, some public health advocates are concerned that the rule contains too many loopholes. An analysis by the Pew Charitable Trusts released last year described how vague product labeling could still allow antibiotics to be abused as growth promoters.
Fast food chains have begun pressuring their livestock suppliers. Last year, Chick-fil-A pledged to buy antibiotic free chickens. Earlier this month, McDonald's promised to buy only chicken treated with antibiotics specific to bird diseases, while avoiding chickens given antibiotics important to human health.
"People may not be aware that the meat that they are eating has been fed antibiotics every day of its life," Laxminarayan told VICE News. "I think it's important to remember that if India and China and Brazil ate meat at the same levels of the US, it would have tremendous consequences for the environment."
Follow Sarah Jane Keller on Twitter: @sjanekeller