San Francisco

SCIENTISTS at the Food and Drug Administration systematically monitor the meat and poultry sold in supermarkets around the country for the presence of disease-causing bacteria that are resistant to antibiotics. These food products are bellwethers that tell us how bad the crisis of antibiotic resistance is getting. And they’re telling us it’s getting worse.

But this is only part of the story. While the F.D.A. can see what kinds of antibiotic-resistant bacteria are coming out of livestock facilities, the agency doesn’t know enough about the antibiotics that are being fed to these animals. This is a major public health problem, because giving healthy livestock these drugs breeds superbugs that can infect people. We need to know more about the use of antibiotics in the production of our meat and poultry. The results could be a matter of life and death.

In 2011, drugmakers sold nearly 30 million pounds of antibiotics for livestock — the largest amount yet recorded and about 80 percent of all reported antibiotic sales that year. The rest was for human health care. We don’t know much more except that, rather than healing sick animals, these drugs are often fed to animals at low levels to make them grow faster and to suppress diseases that arise because they live in dangerously close quarters on top of one another’s waste.

It may sound counterintuitive, but feeding antibiotics to livestock at low levels may do the most harm. When he accepted the Nobel Prize in 1945 for his discovery of penicillin, Alexander Fleming warned that “there is the danger that the ignorant man may easily underdose himself and by exposing his microbes to nonlethal quantities of the drug make them resistant.” He probably could not have imagined that, one day, we would be doing this to billions of animals in factorylike facilities.