While the source of the current salmonella outbreak remains murky, we can reasonably speculate about the genesis of the bug’s drug-resistance: the reportedly endemic overuse of antibiotics by the agricultural industry.

Drugs are given to livestock for multiple reasons. An obvious one is for the treatment of diseases. When livestock are sick, veterinarians administer a significant dosage in hopes of eliminating the animal’s affliction. Another reason is preventative. Animals in close quarters are more susceptible to infection, so farmers will often administer medicine to healthy animals in order to nip anything nasty in the bud. Most controversially, though, members of the agricultural industry use antibiotics for the express purpose of promoting livestock growth.

It’s a well-known, if not entirely intuitive, fact that healthy animals who are fed small, or “sub-therapeutic,” doses of antibiotics will wind up larger than their unmedicated counterparts. In many such cases, these drugs are given to livestock through their feed or water, and without the prescription or oversight of a veterinarian, according to Dr. Gail Hansen, a senior officer at the Pew Campaign on Human Health and Industrial Farming.

An estimated 80 percent of all antibiotics in the U.S. are given to food-producing livestock, according to the FDA. And approximately 83 percent of that medicine is “administered flock- or herd-wide at low levels for non-therapeutic purposes, such as growth promotion and routine disease prevention,” according to a lawsuit filed against the FDA in May. These figures could have very real consequences for public health, because the Catch-22 of this antibiotic abandon is the widespread development of drug-resistant bacteria, colloquially referred to as “super-bugs.”
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In 2006, the European Union banned all use of antibiotics on livestock for growth promotion. And the U.S. Senate will consider similar legislation this year. Sen. Dianne Feinstein, D-Calif., reintroduced the “Preservation of Antibiotics for Medical Treatment Act” last month, which would significantly rein in agricultural drug use, and strictly prohibit the application of sub-therapeutic doses of drugs that have benefits for humans.

Still, the agricultural industry disputes data about its use of antibiotics and the rise of super-bugs, and it has aggressively fought efforts to legislate the matter. As a result, it’s hard to tell how far the legislation might proceed.

How did this happen? The driving forces are Darwin and human carelessness. Bacteria are constantly evolving, adapting to the changing conditions they face. Antibiotics usually kill bacteria. But sometimes a bacteria will develop a biological defense – particularly if too small a dose is used.
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Antibiotics require a prescription in America, but our nation is still very much a part of the problem. Patients routinely demand these drugs, and doctors acquiesce, for respiratory infections and other ailments that will not respond to antibiotics because they are caused by a virus. We use soap with antimicrobial agents when regular soap does equally well. And we allow farmers to feed antibiotics to livestock in horrifying amounts, not to treat illnesses but to make farming more efficient.

This working group, which was part of the Conference on Environmental Health Impacts of Concentrated Animal Feeding Operations: Anticipating Hazards—Searching for Solutions, considered the state of the science around these issues and concurred with the World Health Organization call for a phasing-out of the use of antimicrobial growth promotants for livestock and fish production. We also agree that all therapeutic antimicrobial agents should be available only by prescription for human and veterinary use.

The Alliance for the Prudent Use of Antibiotics (APUA), an advocacy group based in Boston, Massachusetts, published a report in the 1 June 2002 supplement to Clinical Infectious Diseases culminating an expert review of approximately 500 published studies. The report calls for major changes in antibiotic use. Echoing the group’s conclusions, Sherwood Gorbach, a professor of community medicine at Tufts University Medical School in Boston and a member of the APUA’s scientific advisory board, says, “Nontherapeutic use of antibiotics in healthy animals for growth promotion and feed efficiency should be discon- tinued. Furthermore, certain antibiotics that are critically important in human medicine, such as fluoroquinolones and third-generation cephalosporins, should be restricted to use only in critically ill animals and refractory cases under a veterinarian’s prescription.”
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The single greatest factor driving resist- ance to a given antibiotic is simply use of the drug. The more an antibiotic is used, the more the bacteria become resistant to it. For this reason, experts say, antibiotics should be used sparingly, and at dose levels intended to kill all or as many of the bacte- ria causing an infection as possible. If too little antibiotic is used (undertreatment), the most susceptible bacteria are killed off, leaving a hardy group of survivors that grow and multiply into resistant strains.
Human abuse of antibiotics in particu- lar is a major public health problem. Many patients demand anti- biotics routinely, and just as many doctors dispense antibiotics indiscrimi- nately—often for viral infections against which the drugs are useless. And it’s not uncommon for patients to stop taking antibiotics as soon as they feel better, killing only a fraction of the bacteria that are making them sick. Antibiotic use around the world is character- ized by widespread chronic under- treatment.

Chronic undertreatment in agriculture, particularly for non- therapeutic uses no matter how they are defined, is also endemic.