From Google News

Federal health officials reported on Monday that at least two million Americans fall ill from antibiotic-resistant bacteria every year and that at least 23,000 die from those infections, putting a hard number on a serious and growing public health threat. It was the first time that federal authorities quantified the effects of organisms that antibiotics are powerless to fight.

The number of deaths is substantially lower than previous estimates because researchers from the Centers for Disease Control and Prevention stripped out cases in which a drug-resistant infection was present but not necessarily the cause of death.

Infectious disease doctors have long warned that antibiotic resistance threatens to return society to a time when people died from ordinary infections.

"They have come up with hard numbers where it has been only guesswork," said Dr. Stuart Levy, a professor of microbiology at Tufts University and the president of the Alliance for the Prudent Use of Antibiotics. "This sets a baseline we can all believe in."

In 2007, the C.D.C. estimated that about 100,000 people died every year of infections they developed while in hospitals. Most of those infections were believed to be resistant to some antibiotics, but not necessarily the most critical ones. And it was unclear how many of the deaths were caused by the drug-resistant infections. Monday's report quantifies that.

Dr. Steven Solomon, the director of the C.D.C.'s office of antimicrobial resistance, acknowledged that the report underestimated the numbers, but said that was by design. Researchers were instructed to be conservative and to base their calculations only on deaths that were a direct result of a drug-resistant bacterial infection.

"This is a floor," Dr. Solomon said. "We wanted the cleanest number, the least subjective number."

The 114-page report counts infections from 17 drug-resistant bacteria and one fungus, pathogens that Dr. Solomon said caused an overwhelming majority of drug-resistant bacterial infections in the country. It drew on data from five disease-tracking systems, including a major count of bacterial infections reported in hospitals in 10 different areas across the country. The deaths were based on mathematical models — one for each resistant organism.

One point of controversy has been the extent to which industrial-scale animal farming contributes to the problem of antibiotic-resistant infections in humans. The government has estimated that more than 70 percent of antibiotics in the United States are given to animals. Companies use them to prevent sickness when animals are packed together in ways that breed infection. They also use them to make animals grow faster.

The report said that "much of antibiotic use in animals is unnecessary and inappropriate and makes everyone less safe." It also said that about half of antibiotic use in people is inappropriate.

The report divides the pathogens into different levels of urgency to focus public attention on the most dangerous ones.

One particularly lethal type of drug-resistant bacteria, known by its initials CRE, has become resistant to nearly all antibiotics on the market. It is still relatively rare, causing just 600 deaths a year, but researchers have identified it in health care facilities in 44 states. Dr. Thomas R. Frieden, the director of the C.D.C., said its spread could lead to a "nightmare scenario."

"If we're not careful, we'll go the medicine cabinet and it will be empty," he said of the problem of antibiotic resistance.