Medicine: Drugged Chicks Hatch a Menace

More than 19 million lbs. of antibiotics are fed to cattle, pigs and chickens each year as they amble toward the dinner table. At the same time, doctors treating meat-eating humans have seen a steady and alarming increase in infections resistant to these same antibiotics. Is there a link? Scientists and consumer activists long suspected that there was but were never able to prove it.

Now they can. In the first study to connect antibiotic resistance in humans directly with the food we eat, a group of Minnesota public health specialists reported in last week’s New England Journal of Medicine that an eightfold increase in drug-resistant food poisoning among Minnesotans directly followed the approval and use of the same drug in chickens. While most of their patients got sick while traveling overseas–where overuse of antibiotics is even more widespread than in the U.S.–the scientists found evidence that the same thing is happening right here at home.

To be certain that farm animals were the source of the problem, the scientists performed an experiment that mixed molecular genetics with shoe-leather detective work. First they decoded a unique stretch of the resistant bug’s DNA, and then they went shopping. They bought 91 chickens in local markets and, by matching DNA, found that 14% were contaminated with exactly the same bug. Tracking the infections to the source, the scientists discovered that the birds originated not from any single chicken farm but from farms across Minnesota and surrounding states–suggesting that the problem was widespread in the industry. Their conclusion: the antibiotic produced a resistant bug that was passed directly to consumers, probably through poor handling or undercooking. “[The link] is not hypothetical anymore,” says Stuart Levy, director of Tufts University’s center for drug resistance.

What makes the report especially disturbing is that the drug in question is a quinolone–one of a family of antibiotics that, with the spread of penicillin-resistant superbugs, have become the doctor’s first line of defense. The U.S. Food and Drug Administration considers the quinolones so important, in fact, that when the agency approved their use in animals in 1995, it insisted that their manufacturers establish a network to monitor for signs that drug resistance was spreading to humans. The monitoring programs of Abbott and Bayer, however, seem to have been less effective than Minnesota’s, which was the first to notice that the chickens’ antibiotics had come home to roost.

Now that the link has been established, will the FDA cut off the supply of quinolones to animals? Not likely–or at least not right away. Although the FDA is currently forming a plan for pulling antibiotics off farms and ranches when human resistance develops, the agency has yet to establish how much resistance is too much. It may be months before such thresholds are set. Meanwhile, the best advice to consumers is to wash knives, cutting boards and hands after preparing chicken and insist that it be cooked thoroughly, especially when traveling abroad.

–By Dick Thompson/Washington