Salmonella Outbreak Reignites Concern About ‘Super Bugs’ : Dispute Over Banning Drugs in Animal Feed Renewed

The recent outbreak of salmonella poisoning in the Midwest--the largest epidemic ever recorded in the United States--has reignited an old controversy over whether the federal government should outlaw the low-level use of antibiotics in animal feed, a routine practice in the livestock industry since 1950.

The drugs, given to protect the animals from disease and enhance their growth, are believed also to contribute to the development of bacteria strains that do not succumb to most antibiotics. These “super bugs” not only cause disease in animals but are believed to infect humans as well.

S. Dakota to Implement Ban

Today, South Dakota will ban imported livestock from nations that allow animals to be fed the antibiotic chloramphenicol. Gov. William J. Janklow, who announced the ban Friday, said studies show that one in every 20,000 persons may develop a disease that can lead to leukemia after eating meat from animals given the antibiotic.

The FDA bans chloramphenicol for food-producing animals in the United States, but Canada and many other nations permit its use.

The six-state Midwest outbreak of salmonella, which has left two persons dead and more than 16,000 ill since March, was triggered by a strain of bacteria resistant to tetracycline and all forms of penicillin.

Dr. Scott Holmberg, an epidemiologist with the federal Centers for Disease Control in Atlanta, said the bacteria strain that affected the Midwest, transmitted through contaminated milk, “apparently arose from the animal population.”

“These strains may go from herd to herd and from species to species over many months and many miles,” he said. “Sources of salmonella outbreak are usually foods of animal origin. It almost always starts with animals.”

But restricting antibiotics in animal feed might not solve the problem. The imprudent use of antibiotics in humans is acknowledged to play an equal role in the growth of drug-resistant strains.

“The people who are shooting at the amount in animal feed are shooting at a mouse when you’ve got a problem as big as an elephant,” said Dr. Edward H. Kass of Harvard Medical School, a member of a National Academy of Sciences panel that concluded in a 1980 report that it did not have enough data to assess the risk.

“This problem is coming from a great many sources,” Kass said. “To just pick one--which is one of the more trivial--just doesn’t make sense to me.”

Careful Use Urged

The CDC’s Holmberg, who has conducted two studies since 1980 that have established a strong link between human illness and animals fed low doses of antibiotics, agreed that antibiotics must be used carefully, whether in animals or humans.

“We do know that, if you take away the use of antibiotics, you remove strong, selective pressure for the emergence and persistence of antibiotic-resistant strains of bacteria,” Holmberg said. “How soon would we see a decrease in antibiotic-resistant bacteria coming from food animals? No one knows.”

How are these “super bugs” created? Adding antibiotics to animal feed destroys the vulnerable bacteria and allows other strains to survive and multiply. Bacteria not susceptible to drugs reproduce and thrive in the absence of competitors.

For this reason, the Food and Drug Administration first considered banning the use of antibiotics in animal feed in 1977.

Last November, the public-interest Natural Resources Defense Council petitioned the Health and Human Services Department, the FDA’s parent agency, to declare low-level doses of penicillin and tetracycline in animal feed an “imminent” public health hazard and to immediately suspend the practice.

Ordinarily, the FDA cannot take such a step without drawn-out administrative proceedings. Only rarely has it invoked the emergency powers urged by the council to combat a serious public health danger, and it is not expected to do so in this case despite the council’s contention that the “harm need not be immediate.”

However, the FDA is not expected to ignore the issue. The agency has favored a ban since 1977, when Congress directed it to gather more data before proposing one. It asked the National Academy of Sciences to conduct a study, but the academy, after reviewing the existing data, said that it could not come to any solid conclusions.

Dr. Lester Crawford, director of the FDA’s Center for Veterinary Medicine, said in an FDA publication in February that more recent CDC studies “tend to narrow the gap considerably” and “have provided better evidence than we have previously had in the United States tying a specific group of animals from a specific farm to specific cases of human illness.”

One CDC report said that, during salmonella outbreaks between 1971 and 1983, the “case fatality rate was higher for patients infected with anti-microbial-resistant salmonella” than for those infected by bacteria not resistant to drugs. Food animals, it said, were responsible for 11 of 16 drug-resistant cases.

A second CDC study, published last fall in the New England Journal of Medicine, said that a 1983 outbreak of drug-resistant salmonella in four Midwestern states was caused by hamburger from South Dakota cattle fed tetracycline to promote growth.

“This study,” it said, “demonstrates that anti-microbial-resistant organisms of animal origin cause serious human illness and emphasizes the need for more prudent use of anti-microbials in both human beings and animals.”

The FDA’s Crawford said in the agency’s in-house publication: “I think scientific opinion has changed over the past six years, so that at the present time there is support for FDA’s original position.”

Earlier this year, the National Cattlemen’s Assn. surprised other members of the livestock industry by recommending that its members voluntarily discontinue using tetracycline at low-level doses until the federal government resolves the question.

“Even though we believe it’s a safe product--perfectly safe--we believe it’s in our best interest to prevent erosion of consumer confidence in our product,” Tom Cook, a spokesman for the organization, said. “We can get along without it. Because of consumer perception, we’re comfortable with what we did.”

Poultry, veal and hog producers have not gone as far as the cattlemen.

Harvard’s Kass agrees that “super bugs” pose a serious problem but said that regulating antibiotics is not the way to solve it.

“Limiting the use of antimicrobial drugs is not going to lower the rate (of drug-resistant bacteria),” he said. “Nobody is going to deny a sick patient an antibiotic. The only approach that remains is research--to try to understand how bacteria become resistant and then find ways of blocking it.”