Poultry farms' use of antibiotics raises concerns about drug-resistant germs

Hopkins researcher studying effect on humans, environment

August 31, 2004|By Tom Pelton | Tom Pelton,SUN STAFF

Donald Ross worked for years in poultry plants on the Eastern Shore, hanging chickens on hooks, weighing them, packing them and wielding a knife in the "kill room."

About four months ago, he nicked the middle finger on his left hand. The tiny cut should have healed quickly, but it ballooned instead into a festering golf ball-size lesion. Months of antibiotic treatments failed to shrink it, and it had to be surgically removed.

Ross, 46, and a Johns Hopkins Bloomberg School of Public Health researcher suspect his infection was caused by drug-resistant bacteria in chickens at the Temperanceville, Va., plant where he worked. They point to the poultry industry's routine use of millions of pounds of antibiotics to make chickens plumper.

Toxicologist Ellen K. Silbergeld plans to include Ross among more than 100 current and former Eastern Shore poultry handlers in a study of whether the industry's growing use of antibiotics is harming human health and the environment.

Although Ross' injury was minor, Silbergeld says it hints at a broader problem: that antibiotics in chicken feed might be creating tough, drug-resistant bacteria that cling to workers' hands and wash off farms into rivers. Other researchers have found that antibiotic-resistant bacteria are making their way into meat sold in grocery stores.

"This is a very serious issue. I believe there is a lot of antibiotic-resistant bacteria that is getting out into the community and into the environment, and nobody is paying attention to what it's doing," said Silbergeld, who has also studied lead poisoning in Baltimore and mercury contamination in the Amazon.

Antibiotics in animal feed have become a national concern, with McDonald's restaurants recently pledging to work with poultry suppliers to phase out growth-promoting antibiotics that are also used in human medicine.

The drugs are a significant issue for the poultry industry on the Delmarva peninsula, which last year included 1,900 farms selling 576 million chickens that were processed by 14,100 workers.

Richard L. Lobb, spokesman for the National Chicken Council, a trade group that represents companies that process most of the 8.7 billion chickens sold in the United States every year, defended the industry's use of antibiotics.

Farmers have been routinely adding microbe-killing formulas to chicken feed since the 1950s, Lobb said.

When a few birds develop bacterial infections, farmers add antibiotics such as virginiamycin and tetracycline to the drinking water of an entire flock, which can often exceed 200,000 birds, Lobb said. Farmers then wait a number of days specified by the drug makers before selling the birds to prevent medications from being passed on in the meat, he said.

"There's been a lot of rhetoric about this issue, but there's not a lot of science to back it up," Lobb said. "Decades of use of virginiamycin in animals, for example, has resulted in no impact on human health."

But representatives of poultry workers insist that there is a link between workers' health problems and antibiotics.

Pilot study

A pilot study Silbergeld conducted on 60 poultry workers in the areas of Pocomoke City and Georgetown, Del., two years ago found that 80 percent of them were carrying bacteria from the intestines of chickens. And 60 percent of the workers had antibiotic-resistant strains of the bacteria, compared to 10 percent of the general population in those locations, she said.

Her new study will involve interviews with current and former workers, examinations of their medical records, lungs, blood and stool samples. She will also study some of their family members and neighbors to determine how often they suffer stomach or intestinal illnesses.

To assess the impact on the environment, Silbergeld is also testing catfish caught in the Pocomoke River for antibiotic-resistant bacteria. The presence of the bacteria would be evidence that microbes from chicken manure are being washed into the river from farms, which use the manure as fertilizer.

By sampling bacteria from the hands of fishermen, Silbergeld hopes to discover if they are also being exposed to drug-resistant bacteria from chicken farms.

Of the first 15 catfish she and her colleagues caught, four had drug-resistant strains of bacteria with the same genetic markings as germs found in chicken intestines.

"There are about a billion chickens being raised on the Delmarva peninsula, and each of them produces about 2.5 pounds of waste. That's 2.5 billion pounds of waste going out into the environment," Silbergeld said. "We're basically following the bacteria in the chicken waste."

A 2001 study by the U.S. Food and Drug Administration and the University of Maryland found that a fifth of 200 samples of ground chicken, beef, turkey and pork sold in supermarkets in the Washington area were contaminated by salmonella, which causes food poisoning. And 84 percent of these bacteria samples were resistant to antibiotics.

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