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Volume 2 Published - 14:00 UTC    08:00 EST    05-February-2001      
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Back To Vidyya Antibiotic Resistance

From Down On The Chicken Farm

Chicken wings and turkey drumsticks are almost as ingrained in American culture as apple pie and baseball. But the lip-smackin', finger-lickin' good taste is less palatable when the poultry makes people sick. Even harder to swallow are germs that don't respond to drugs that may be prescribed to fight the sickness.

New evidence that drugs used in poultry can cause antibiotic-resistant infections in consumers spurred the Food and Drug Administration's Center for Veterinary Medicine (CVM) to take action. On October 31, CVM proposed to withdraw the approval of an antibacterial, Baytril (enrofloxacin), used to treat disease in chickens and turkeys. CVM approved Baytril in 1996. Made by the Bayer Corporation of Shawnee Mission, Kan., Baytril belongs to a class of antibacterials called fluoroquinolones, which have been used in humans since 1986.

Shortly prior to CVM's announcement, Abbott Laboratories of North Chicago, Ill., requested withdrawal of the approvals for its poultry fluoroquinolone products. This means that Abbott will voluntarily remove these products, trade name SaraFlox, from the market.

The Bayer Corporation has requested a hearing to present safety data to try to keep Baytril on the market. The company must submit all data and analysis to support consideration for a hearing by January 2, 2001.

Poultry growers use fluoroquinolone drugs to keep chickens and turkeys from dying from Escherichia coli (E. coli) infection, a disease that they could pick up from their own droppings. But the size of flocks precludes testing and treating individual chickens--so when a veterinarian diagnoses an infected bird, the farmers treat the whole flock by adding the drug to its drinking water. While the drug may cure the E. coli bacteria in the poultry, another kind of bacteria--Campylobacter--may build up resistance to these drugs. And that's the root of the problem.

People who consume chicken or turkey contaminated with fluoroquinolone-resistant Campylobacter are at risk of becoming infected with a bacteria that current drugs can't easily kill. Campylobacter is the most common bacterial cause of diarrheal illness in the United States, according to the Centers for Disease Control and Prevention. It's estimated to affect over 2 million persons every year, or 1 percent of the population.

Commonly found in chickens, Campylobacter doesn't make the birds sick. But humans who eat the bacteria-contaminated birds may develop fever, diarrhea, and abdominal cramps. In people with weakened immune systems, Campylobacter can be life-threatening. Eating undercooked chicken or turkey, or other food that has been contaminated from contact with raw poultry, is a frequent source of Campylobacter infection. Not washing utensils, countertops, cutting boards, sponges, or hands after coming into contact with raw poultry can also spread the bacteria and cause infection. People infected with Campylobacter may be prescribed a fluoroquinolone--which may or may not work.

But the damage doesn't stop there. "Cross-resistance occurs throughout this class of drugs," says Stephen F. Sundlof, DVM, PhD, director of CVM. "So resistance to one fluoroquinolone can compromise the effectiveness of all fluoroquinolone drugs."

Considered one of the most valuable drug classes available to treat human infections, fluoroquinolones are used to treat a wide range of diseases, including the gastrointestinal illness caused by Campylobacter infection.

The use of antibiotics in food animals has been a human health concern since the 1970s when FDA first called for restrictions on antibiotics used in animal feed. Prior to 1995, when fluoroquinolones were first approved to treat poultry, very few fluoroquinolone-resistant Campylobacter were found in people with foodborne diseases in the United States. After the approval, however, many more fluoroquinolone-resistant bacteria were found in humans and in poultry from slaughter plants and retail stores.

The data to support these findings came from a study by the Minnesota Department of Health and a computerized system called NARMS--the National Antimicrobial Resistance Monitoring System. Created in 1996 as a joint effort by CVM, CDC, and the U.S. Department of Agriculture, NARMS monitors human and animal resistance to 17 antimicrobials. Antimicrobials include antibacterials, antivirals, antifungals, and antiparasitics.

Data provided by NARMS and other sources were used to develop a risk assessment. This assessment, along with other data, supported CVM's decision to propose the withdrawal of approval of Baytril for use in poultry. The risk assessment quantified, for the first time, the magnitude of the dangers to humans eating chicken contaminated with fluoroquinolone-resistant Campylobacter. It showed that the number of people infected with fluoroquinolone-resistant Campylobacter from eating chicken rose from an estimated 8,782 in 1998 to 11,477 in 1999.

The risk assessment, completed in October, is only one action CVM has taken to address the antimicrobial resistance problem over the years, says Sundlof. Another part of CVM's proactive program is its proposal to take a stronger regulatory approach when approving new antimicrobial drugs for use in food animals. A "framework document" lays out a plan for evaluating the safety of these drugs based on their importance to human health. If the plan is implemented, the drugs of highest importance--those used to treat a serious or life-threatening disease in humans for which there is no effective alternative treatment--would be subject to the strictest criteria for approval for animal use. Among the studies that would be required by drug sponsors are tests to show their product's potential to induce antibiotic resistance.

CVM has invited input from outside experts on the principles in the framework document. Two public meetings have been held in the past year and a half, and a third is scheduled for January 23-24 to discuss establishing resistance thresholds in food-producing animals. The workshop will be held from 8:30 a.m. to 5:00 p.m. at the DoubleTree Hotel, 1750 Rockville Pike, Rockville, MD 20852. For more details on the meeting and the framework document, see the CVM Home Page at www.fda.gov/cvm/.

"FDA and CVM will continue to work to put in place a regulatory system that addresses the dangers of antimicrobial resistance and offers better protection to public health," says Sundlof. "At the same time, CVM will strive to assure the safe use of antimicrobial drugs in food-producing animals."

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Editor: Susan K. Boyer, RN
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