Washington -- The Centers for Disease Control on Monday confirmed a link between routine use of antibiotics in livestock and growing bacterial resistance that is killing at least 23,000 people a year.

The report is the first by the government to estimate how many people die annually of infections that no longer respond to antibiotics because of overuse in people and animals.

CDC Director Thomas Frieden called for urgent steps to scale back and monitor use, or risk reverting to an era when common bacterial infections of the urinary tract, bloodstream, respiratory system and skin routinely killed and maimed.

"We will soon be in a post-antibiotic era if we're not careful," Frieden said. "For some patients and some microbes, we are already there."

The discovery of penicillin in 1928 transformed medicine. But because bacteria rapidly evolve to resist the drugs, and resistance is encouraged with each use, antibiotics are a limited resource.

2 million infections

Along with the annual fatalities, the report estimated at least 2 million antibiotic-resistant infections occur each year. Frieden said these are "minimal estimates" because they count only microbes that are resistant to multiple antibiotics and include only hospital infections, omitting cases from dialysis centers, nursing homes and other medical settings.

At least 70 percent of all antibiotics in the United States are used to speed growth of farm animals or to prevent diseases among animals raised in feedlots. Routine low doses administered to large numbers of animals provide ideal conditions for microbes to develop resistance.

"Widespread use of antibiotics in agriculture has resulted in increased resistance in infections in humans," Frieden said.

The pharmaceutical and livestock industries have long disputed any such linkage. But the report called for phasing out such uses.

"Of the 18 specific antibiotic-resistant threats discussed in the report, only two have possible connections to antibiotic use in food animals," said the Animal Health Institute, a lobbying group that represents pharmaceutical companies.

Steve Heilig, public health director for the San Francisco Medical Society, said the report "clearly implicates agriculture's contribution to the problem." The big question, he said, is whether leaders in agriculture and government "will finally listen to their own expert agency on this."

Patients who insist on antibiotic treatments are another big problem - the report said half of antibiotic use in humans is unnecessary.

"Patients demand antibiotics and feel their doctor has not done an adequate job if they don't get a prescription," Frieden said.

Wide implications

Beyond turning common infections deadly, the rise of antibiotic resistance would undermine much of modern medicine. Organ transplants, joint replacements, cancer therapies and the use of catheters, respirators and other invasive procedures and devices would be impossible because of the risk of infection.

The link between overuse of antibiotics in livestock and microbial resistance has been suspected since the 1960s, but Congress, at the behest of the pharmaceutical and livestock industries, has blocked efforts by the Food and Drug Administration to scale back their use.

The agency in April 2012 asked drugmakers to voluntarily stop using antibiotics to promote growth in animals but has not issued final regulations. The agency does not plan any restrictions on routine low doses to prevent infections in animals.

Francis Scarpulla, owner of Lost Coast Farms, a small organic sheep and beef ranch in Humboldt County that does not use antibiotics, said commercial livestock have to be fed the drugs because of the crowded conditions in which they are raised.

"If you have a healthy cow foraged on grass, and if they are in a clean field environment, your cows are not going to get sick," he said. "When you cram them into huge feedlots, they start getting sick because there are too many of them in too small a space."

Legislation goes nowhere

Organic certification prohibits antibiotic use, but raising such animals is costly, he said.

Rep. Henry Waxman, D-Los Angeles, first introduced legislation in 1980 to restrict antibiotic use in livestock. For the past decade, Rep. Louise Slaughter, D-N.Y., has introduced similar bills, joined in recent years by Sens. Dianne Feinstein, D-Calif., and Kirsten Gillibrand, D-N.Y., but the measures have gone nowhere.

"We constantly hear from the pharmaceutical and livestock industry that antibiotic use in livestock is not a problem and we should focus on human use," said Avinash Kar, a staff attorney at the San Francisco office of the Natural Resources Defense Council, an environmental group that has sued the FDA to force it to ban using antibiotics to promote growth in livestock. The case is now pending before the 2nd U.S. Circuit Court of Appeals.