AN IN-depth hearing in the US last week shed new light on the controversy surrounding antibiotic resistance and concerns about a potential link to the use of subtherapeutic antibiotics in food animal production.
It pitted scientists on both sides of the issue in a debate that unveiled the lengthy history and conflicting views of the science behind the hot topic.
While the livestock industry has been dubious about the science linking antibiotic resistance to livestock production, several expert witnesses from the medical and public health fields concluded that a scientific link was "unequivocal" based on studies in both the US and Europe. The written testimony from those witnesses cited numerous peer-reviewed studies in lengthy bibliographies.
The hearing was the third in a series as the committee "examines the growing and serious problem of antibiotic resistance," committee chair Henry Waxman (D., Cal.) said in opening remarks.
The first two hearings explored the issue of antibiotic resistance, including its complex mechanisms and the resistance arising from the use of human antibiotics. Waxman noted that last week's hearing on animal agriculture covered a "complicated and controversial" issue.
Centers for Disease Control & Prevention director Dr Thomas Frieden sent a letter for the subcommittee's record restating his testimony from the second hearing and discussing "the strong scientific evidence of a link between antibiotic use in food animals and antibiotic resistance in humans".
He said some of his discussion from the earlier hearing had been "mischaracterised". Indeed, it was widely reported that he had said he did not know of studies showing such a link.
In his letter to health subcommittee chair Frank Pallone Jr. (D., N.J.), Frieden wrote that "there are multiple North American studies describing how: (1) use of antibiotics in animals results in resistant bacteria in food animals, (2) resistant bacteria are present in the food supply and transmitted to humans and (3) resistant bacteria result in adverse human health consequences (such as increased hospitalisations)".
The three hearings come at a time when the subcommittee is under pressure to pass legislation addressing antibiotic resistance that endangers the health of people and animals.
At the hearing, several witnesses in the medical and public health community voiced strong support for the Preservation of Antibiotics for Medical Treatment Act (PAMTA) and for the Food & Drug Administration's new "Draft Guidance #209" on the use of antimicrobials in animal agriculture.
Two witnesses from the University of Minnesota illustrated the complexity of the scientific debate.
Dr. James Johnson, a board-certified infectious disease specialist who teaches at the university's School of Medicine, said in written testimony, "The evidence of a cause-and-effect link between food animal antibiotic use and drug-resistant infections in humans is broad ranging and derives from numerous epidemiological, molecular epidemiological, ecological and experimental studies."
Johnson, who testified on behalf of the Infectious Diseases Society of America (IDSA), the professional society representing 9000 US infectious disease specialists, added "the threat to humans due to antibiotic use in animal agriculture includes both acquisition of resistant pathogens by humans (whether from the food supply, direct contact with animals or environmental sources) and transfer of resistance genes from animal to human bacterial populations".
"A broad consensus exists among relevant experts that, based on the available evidence, it is reasonable and prudent to conclude that the use of antibiotics in animal agriculture poses an important threat to human health that warrants urgent action," he said.
His testimony was documented with extensive references and web sites of juried papers.
"To better protect our patients and the general public against antibiotic-resistant bacterial infections, IDSA strongly supports efforts to eliminate all non-judicious uses of antibiotics in human medicine and animal agriculture" such as PAMTA and FDA's recent draft guidance, Johnson testified.
Dr. Randall Singer, a veterinarian with a doctoral degree in epidemiology who is an associate professor of infectious disease epidemiology and ecology at the University of Minnesota, took a different scientific view.
Singer, who has studied antibiotic resistance in human and animal health for the past 12 years, defended what he calls "low-dose" use of antibiotics in food animal production.
In his testimony, he pointed out that "many of the antibiotics currently used in animal agriculture, particularly those used for 'production purposes,' were approved in the 1960s. ... We now know that low-dose uses of antibiotics improve the overall health of the growing animal, and the outdated label claims of feed efficiency and growth promotion do not do justice to the 'gut health' and 'disease prevention' attributes that these low doses possess. In general, the improvements seen in feed efficiency and growth are the result of improved health and gut integrity due to disease prevention."
Singer said, "All uses of antibiotics improve animal health, and these improvements in animal health can substantially improve human health."
However, he added, "All uses of antibiotics may also pose a risk mainly associated with increases in antibiotic resistance. The key is to assess the ability of interventions to maximize the benefits and minimize the risk associated with the agricultural use of antibiotics."
Singer's testimony concerning low-dose use of antibiotics for growth promotion and feed efficiency was an open reference to FDA's draft guidance issued in June aimed, in fact, at banning over-the-counter antibiotics used solely for growth promotion and feed efficiency (Feedstuffs, July 5).
That guidance, which is open for public comment until Aug. 30, would end those "production" uses, saving antibiotics only for actual animal health applications, and would require that veterinarians oversee all uses of antibiotics for animal health.
Animal Health Institute vice president Dr. Richard Carnevale, a veterinarian and former FDA new animal drug regulator, testified that "in response to concerns raised in the 1970s, FDA required sponsors to conduct tests to determine the potential for resistance to be selected in the animals and to be transferred to bacteria that could cause human disease".
Carnevale, whose organisation represents companies that manufacture animal health drugs, said "while the standards and science may have changed over the years, the safety of these products has been continually demonstrated as an ongoing exercise at FDA".
Carnevale testified that "antibiotics are highly regulated and are used carefully by veterinarians and livestock and poultry producers".
"FDA's regulatory process and risk assessment are the proper tools for making decisions about the use of these products," he said.
Noting the new FDA draft guidance, Carnevale said, "The industry is committed to working collaboratively with the agency to address these concerns while assuring the availability of important animal health products to prevent, control and treat animal disease."
However, Dr. Stuart Levy, a professor of molecular microbiology at Tufts University and a past president of the 40,000-member American Society for Microbiology, was not swayed.
Levy, who has researched resistance for three decades and heads the Alliance for the Prudent Use of Antibiotics, worried that FDA's guidance would not be effective - at least not soon enough.
It "represents only voluntary guidelines that would take many months, perhaps years, to finalise," Levy testified. "Even if finalised as a voluntary guidance to industry, the reality is that agribusiness has fought efforts to curtail overuse of antibiotics every step of the way, and there is no basis for confidence that industry will do anything but dodge and challenge FDA's guidance.
"Because most antibiotics currently approved for growth promotion are also approved for routine disease prevention, I have great concerns that industry will continue feeding massive quantities of antibiotics non-therapeutically, rendering meaningless the FDA guidance on eliminating antibiotic use as growth agents," Levy said.
He, too, endorsed PAMTA.
House Rules Committee chair Louise Slaughter (D., N.Y.) told reporters on a press call last week that she will continue to seek co-sponsors for PAMTA. She said 113 Democrats have signed on, but no Republicans. When she nears the 218 needed for passage, she intends to discuss a vote on her bill with House Speaker Nancy Pelosi (D., Cal.), she said.
Slaughter praised the House energy and commerce subcommittee for addressing the antibiotic issue, but when asked if she would merge her bill with legislation drafted in the subcommittee, she was cautious, saying, "I don't want PAMTA to be watered down."
Slaughter indicated that she would work for passage of the bill in a lame-duck session expected to be held after the November midterm elections, noting that Republican victories could stymie action.
The hearing testimony, Frieden's letter and archived webcasts are online at www.energycommerce .house.gov.