Courtesy of San'an Nie Pigs in a commercial farm in China

Back in 2005, when I was a reporter based out of TIME’s Hong Kong office, I spent more time than I care to remember in the backyard chicken farms of Asia. This was the time of the H5N1 avian flu, which broke out regularly in chickens and occasionally (with fatal effects) in human beings and which always seemed to be one click of the genetic lock away from threatening the entire world. To prevent that mutation from happening — one of that would have allowed the deadly H5N1 virus to spread easily from person to person, like a human flu virus — health officials in affected countries would do their best to track and eradicate outbreaks as they occurred in animals, often by simply culling an afflicted flock.

But there was always one country where that plan never quite worked: China. Chinese chicken farmers had an unfortunate habit of prophylactically dosing their birds with Tamiflu, the only antiviral drug that showed any effectiveness against H5N1. (U.S. preparations for a possible bird-flu pandemic included stockpiling millions of doses of the drug.) As a result, it became that much more difficult for health officials to track H5N1 outbreaks because Tamiflu-dosed chickens could still get infected and spread the virus but without showing the symptoms that would set off medical alarm bells. And overusing Tamiflu also eroded its effectiveness as over time the H5N1 virus was able to develop a resistance to the drug. Had an H5N1 human pandemic ever occurred, we may well have been helpless.

In the years since, you might have hoped that Chinese farmers had learned to be a bit more judicious when it comes to dealing out high-end human drugs to their animals — but that’s not the case. A new study in the Proceedings of the National Academy of Sciences shows that China, already the world’s largest producer and consumer of antibiotics, is heavily using the drugs in animals as a way to enhance growth and prevent disease in crowded conditions. And just as happened with the overuse of Tamiflu, China’s animal drug addiction is leading to increasing antibiotic resistance, which in turn could lead to serious problems for people who depend on those drugs to fight infections. “It’s urgent that we protect the effectiveness of our current antibiotics because discovering new ones is extremely difficult,” said Zhu Yongguan, a researcher with the Chinese Academy of Sciences and the lead author on the PNAS paper. “Multidrug resistance is a global problem and must be addressed in a comprehensive manner.”

It’s no secret that Chinese farmers use high levels of antibiotics in animal feed. The question for researchers is whether that might be a direct cause of increasing antibiotic-resistant infections in humans. For the PNAS paper, researchers actually sifted through the manure-enriched soil found near three large-scale Chinese pig farms, searching for the presence of antibiotic-resistant genes. (The medicine tends to be poorly absorbed by the animals, and so much of it does end up in the manure.) It wasn’t hard to find them. Researchers counted 149 unique antibiotic-resistant genes, some at levels 192 to 28,000 times higher than control samples. Since the manure is often sold as fertilizer or washes downstream into rivers, those antibiotic-resistant genes can spread to other forms of bacteria, decreasing the overall effectiveness of the drugs in human beings.

But Chinese farmers are hardly alone in their reliance on drugs, as new numbers from the U.S. Food and Drug Administration (FDA) last week showed. In 2011, 29.9 million lb. of antibiotics were sold in the U.S. for meat and poultry production — nearly four times the amount sold to treat sick people. And most of the animals taking the drugs likely aren’t sick; as in China, the antibiotics are used for growth promotion and to help the pigs or chickens survive crowded conditions on industrial farms.

At least that’s what we think — producers of meat and poultry aren’t required to report how they use the drugs, which drugs they use, on which animals and in which quantities. That makes it difficult for scientists to directly connect the heavy use of antibiotics in animals with antibiotic resistance in people. In a New York Times story last year, one public-health researcher compared the lack of data collection to “facing off against a major public health crisis with one hand tied behind our backs.” But efforts by the government in the past to more tightly regulate antibiotics in animals have met with failure, thanks in part to powerful agriculture interests.

There’s some hope: last year the FDA issued draft guidelines that would ask the pharmaceutical industry to change labeling and marketing practices so that antibiotics would be used only on sick animals, rather than for growth promotion on healthy ones. But even those guidelines would only be voluntary. In China and in the U.S., drugs are likely to remain a part of commercial meat production — and the rest of us may pay the price.