US Factory Farm Antibiotic Use Threatens Public Health

Do livestock breed drug-resistan bugs? Antibiotics on farms may
threaten humans; and Public health

(U.S. News & World Report; 05/31/99)

Kirk Smith has chicken on his mind. Chicken, that is, that the Minnesota
epidemiologist purchased in his local supermarkets.

Smith's analysis of bacteria in that poultry, published last week in the
New England Journal of Medicine--along with unpublished data from the Centers
for Disease Control and Prevention--gives new scientific heft to earlier
research linking antibiotic use in agriculture to drug-**resistant** pathogens in
animals. Further, the findings point to an alarming corollary: **Resistant**
strains threaten medicine's ability to treat human disease.

Most troubling are **antibiotics** approved for animal use that belong to
the same classes of drugs needed for curing people. These include all of
the fluoroquinolones, vancomycin, and a new drug, Synercid, soon to be approved
by the U.S. Food and Drug Administration. Farmers use the drugs to spur faster
growth and treat livestock diseases. But while most bacteria exposed to the
**antibiotics** are killed, at least a few survive. These **resistant** bugs
multiply and can be passed to humans through raw or undercooked food, water,
and manure. According to an editorial accompanying the NEJM report, "decades
of {antibiotic} use in animals have created a huge reservoir of
**resistant** bacteria . . . with a potential to spread to humans."

From 1992 to 1998, Smith and others at the Minnesota Department of Health
studied bacterial cultures from residents infected by Campylobacter jejuni,
a microbe that causes an estimated 2 million to 8 million cases of
gastroenteritis in the United States annually. In 1992, only 1.3 percent of
Minnesota's cases were caused by strains of campylobacter that were
**resistant** to fluoroquinolones, among the most useful drugs for treating
serious foodborne infections. By 1998, **resistance** had grown to 10.2

Smith realized that about 75 percent of the **resistant** cases in 1996-97
were associated with foreign travel. A little more medical sleuthing showed
that about half of those travelers had been to Mexico, where fluoroquinolone
use in poultry increased almost fourfold between 1993 and 1997.

Chickens fingered. But a significant number of Minnesotans who had stayed
home also developed **resistant** infections, particularly from 1996 to 1998.
Enter the chickens: Two fluoroquinolone drugs had been approved for treating
E. coli in U.S. chickens in 1995 and 1996. Out of 91 chicken products Smith
purchased from 16 supermarkets and analyzed for the new study, 80 were
contaminated with campylobacter. Twenty percent of these bugs were
**resistant** to ciprofloxacin, a fluoroquinolone often used for treating
severe gastroenteritis. DNA fingerprinting matched **resistant** strains
from the chickens to **resistant** strains in sick Minnesotans.

Vancomycin-**resistant** enterococci, or VRE--a bug **resistant** to
nearly all available **antibiotics**--has also become a serious problem. First
found in Europe, where its spread was linked to an antibiotic growth promoter,
VRE arrived here in the 1990s and has proved deadly in many U.S. hospitals.
Searching for a cure, the pharmaceutical company Rhone-Poulenc Rorer
developed Synercid.

But according to CDC scientists, a related antibiotic, virginiamycin,
used since 1974 in chickens has spread bugs that are **resistant** to Synercid
even before the drug is approved. Examining bacteria from human stool samples,
the researchers found that some individuals already carry Synercid-**resistant**
bugs. And an analysis of chicken products from three states showed that
Synercid- **resistant** enterococci contaminated more than half the products,
says CDC's Fred Angulo, who will present the data this week in Washington,

By the end of summer, the FDA plans to complete an assessment of the
dangers posed by fluoroquinolone-**resistant** campylobacter. The agency is also
drafting new regulations that may radically restrict how animal
**antibiotics** are tested and used in the future. John Keeling of the
Animal Health Institute, a pharmaceutical trade group, says no action should be
taken until more data demonstrate a significant risk to humans. But five consumer
groups, led by the Center for Science in the Public Interest, believe we
already know enough: They have petitioned the FDA to ban **antibiotics**
used for animal-growth promotion that are needed to treat human illness.

(Copyright 1999)