Public health advocates are fuming over a new court ruling that they say could hasten the coming of the next pandemic.

In a 2-1 decision released Thursday, the U.S. Court of Appeals for the 2nd Circuit ruled that the U.S. Food and Drug Administration need not consider banning the use of antibiotics in healthy food-producing animals.

"We believe that this decision allows dangerous practices known to threaten human health to continue," said Avinash Kar, an attorney with the Natural Resources Defense Council. "Adding antibiotics to farm animals' feed, day after day, is not what we should be doing. It's not what the doctor ordered and it should not be allowed."

In March 2012, a federal court ruled that the FDA must act on scientific knowledge that the overuse of antibiotics in animals raised for food has contributed to the rise of antibiotic-resistant infections in humans. That decision came in response to a lawsuit filed by the NRDC concerning findings made by the FDA back in 1977. Feeding livestock low doses of penicillin and most tetracyclines, the agency had concluded, might pose a risk to human health. The FDA never acted on or retracted those findings.

"This is a first and important step," Kar told The Huffington Post in 2012. "But the fight is not completely won."

Kar's remark proved prescient with this week's court decision. Thursday's finding overturns two district court rulings in cases brought by the NRDC and other groups that would have compelled the FDA to withdraw approval for most non-therapeutic uses of penicillin and tetracyclines in livestock -- unless drug makers could prove those substances were safe.

The fight is still not over, according to Kar, who said that he and his colleagues are "looking at all options, including legal ones."

In recent years, leading public health experts and agencies have sounded the alarm over the declining effectiveness of antibiotics in human medicine and the resulting increased threat of Methicillin-resistant Staphylococcus aureus (MRSA) and other difficult-to-treat infections.

In April, the World Health Organization released a report warning that a "post-antibiotic era, in which common infections and minor injuries can kill, far from being an apocalyptic fantasy, is instead a very real possibility for the 21st century." Last year, the U.S. Centers for Disease Control and Prevention estimated that at least 2 million people in the U.S. become infected with antibiotic-resistant bacteria each year, with at least 23,000 succumbing to their illnesses. A White House advisory committee is expected to issue a report on the topic in the next few weeks.

Authorities generally agree that the predicament is a result of antibiotic overuse in both humans and animals. As the appeals court noted in its opinion, "for each dose of antibiotics given to humans for medical purposes, four doses are given to livestock for non-medical reasons to encourage faster, healthier growth."

This use of small amounts of antibiotics for large groups of animals over long periods of time can create ideal conditions for bacteria to develop resistance. Bacteria that can withstand the drugs will survive and reproduce, while bacteria susceptible to the drugs will die off. It's a microscopic survival of the fittest.

In his dissenting opinion, Judge Theodore Katzmann compared the federal government's response on this issue to how it has dealt with global warming.

Much like climate change, there is overwhelming scientific consensus, even acknowledged by the court's majority and by the FDA, that antibiotic resistance threatens human health and that overuse of the drugs in livestock contributes to the development of this resistance. Yet in 2011, the U.S. Environmental Protection Agency refused to declare whether greenhouse gas emissions from motor vehicles endangered public health, in part because, as Katzmann writes, the agency believed that "regulating motor vehicle emissions would not be an effective means of addressing global warming."

"Each individual animal dose of antibiotics may not endanger human health," wrote Katzmann, "but that is no reason to think that Congress gave the agency discretion to ignore the larger problem."

Meanwhile, the Animal Health Institute, which represents pharmaceutical companies, called Thursday's ruling a "welcome development."

The group highlighted the FDA's current voluntary guidance, which offers suggestions to the pharmaceutical industry on the use of antibiotics in livestock, rather than imposing a ban. "As FDA recently reported, all 26 companies affected by the policy have pledged to align their products with the effort and changes have begun," Ron Phillips, a spokesman for the institute, told HuffPost in an emailed statement. "As a result of this policy being implemented, all medically important antibiotics used in food animals will be used to fight disease at the direction of a veterinarian."

"We believe this decision will clear the way and allow FDA to focus on working with stakeholders to successfully implement this policy in a timely manner," Phillips' email continued.

But the guidelines' voluntary nature leaves critics uneasy.

"Many companies, if they chose to, could back out," said Kar.

Perhaps more concerning, he added, is what he calls a language "loophole" in the guidance: While a company might stop feeding healthy animals low doses of antibiotics directly for growth promotion, they could still add the drugs to animal feed under the pretext of illness prevention. "The same uses can continue under a different name," he said.

Dr. David Wallinga, founder and director of the nonprofit Healthy Food Action, highlighted a potential case in point. Last week, Cargill, Inc., one of the nation's biggest turkey producers, announced plans to stop using antibiotics as a growth promoter in turkeys.

"Ending the use of antibiotics for the sole purpose of growth promotion is our first step in providing consumers with expanded turkey options at an affordable price," Mark Klein, a spokesman for Cargill, told HuffPost in an email.

Wallinga was skeptical. "On the face of it, that sounds great," he told HuffPost. "But Cargill doesn't say they are not going to use antibiotics in feed to prevent disease."

Indeed, Klein's email went on to note that antibiotics allow the company to "prevent, control and treat" disease in its turkey flocks, and added that "antibiotics will still be administered under the direction of a veterinarian."

The pharmaceutical company Novartis has also ceased making growth-promotion claims about its swine drug Denagard. However, as critics point out, there are still references to "daily gain," "performance" and "profitability" on the drug's website, which could lead farmers to continue using the drug -- at least indirectly -- to fatten up pigs faster. Novartis did not response to a request for comment.

Steven Roach, food safety program director with the nonprofit Food Animals Concerns Trust, one of the groups advocating for more stringent behavior on the part of the FDA, has been tracking Novartis' materials.