That may be part of the problem, Lawrence said, but "increasing evidence suggests that other pathways are more important."
According to the best estimates of researchers in the Union of Concerned Scientists, far more antibiotics (27.6 million pounds a year) are given to livestock for growth promotion than are to given humans (4.5 million pounds a year). (Statistics by the industry-related Animal Husbandry Institute differ greatly from the scientists' numbers; see infobox on Page B5.)
Lawrence said the conditions in confinement operations where the animals receive the antibiotics are just right for building drug-resistant bacteria because there is failure of infection control (the animals are crowded and hygiene isn't optimal) and there is widespread, prolonged exposure to antibiotics with little dose control.
A graduate student at the Center for a Livable Future at the Bloomberg School of Public Health at Johns Hopkins University in Baltimore, Md., where Lawrence is director, tested the air in a Maryland swine confinement facility and found 137 presumptive Enterococcus species, as well as a number of other bacterial species. Almost all of them - 98 percent - were multi-drug resistant; some were resistant to four antibiotics.
The drug-resistant bacteria can find their way to humans through runoff from the farm sites or through the meat, and Lawrence gave several examples of human bacterial infections that had been traced back to livestock sources.
The use of the same antibiotics in humans and livestock "is something that never should have been permitted, in my view," Lawrence said. It is "creating a problem of enormous proportions in the area of antibiotic resistance."
One reason the use of antibiotics in confinement facilities has not been targeted for better regulation indicates a bigger problem in the system.
"At the federal level, the agencies responsible for public health and the agencies responsible for food systems haven't done much cross talking," Lawrence said.
The National Antimicrobial Resistance Monitoring System is managed by the Centers for Disease Control and Prevention, and the Food and Drug Administration. There is no cross talk with the Department of Agriculture, Lawrence said.
He suggested that millions of dollars in campaign donations by the pharmaceutical industry also might have something to do with the lack of regulation.
However, Lawrence said he is encouraged by increasing public awareness of the issue recently, as shown by the popularity of foods labeled antibiotic-free. Stonyfield Farms, for example, has resurrected the Vermont dairy industry in its quest to meet the demand for its antibiotic-free yogurt, he said.
Lawrence's lecture was sponsored by ISU's Leopold Center for Sustainable Agriculture.
Heidi Marttila-Losure can be reached at 232-2161, Ext. 352, or firstname.lastname@example.org.
Antibiotic use in the United States (2002)
Dr. Robert Lawrence says the following numbers are an example of two groups looking at the same situation and finding different answers: The Animal Husbandry Institute, an industry-related group, says far more antibiotics are used for humans than for animals. The Union of Concerned Scientists, which has to estimate the numbers for animal use because the actual numbers are proprietary, reaches a far different conclusion.
For growth promotion in food animal production:
* 3.1 million lbs/yr (AHI)
* 27.6 million lbs/yr (UCS)
For "prophylaxis" and disease treatment in food animal production:
* 14.7 million lbs/yr (AHI)
* 2.0 million lbs/yr (UCS)
For use by humans:
* 32.3 million lbs/yr (AHI)
* 4.5 million lbs/yr (UCS)