Figure 1. Distribution of ciprofloxacin MICs among Campylobacter jejuni isolated from humans and retail chicken. A, human isolates, 1997–2001; N = 1,471. B, grocery store purchased chicken iso- lates, 1999; N = 62. may be a source of domestically acquired ciprofloxacin- resistant Campylobacter infections; 10% of retail chickens were contaminated with ciprofloxacin-resistant Campylo- bacter. Other studies have shown that Campylobacter, including ciprofloxacin-resistant Campylobacter, are com- monly isolated from retail poultry meats. A survey of retail meats purchased in the Washington, D.C., area isolated Campylobacter species from 71% of chicken and 14% of turkeys tested; (36) 25% of the C. jejuni isolates and 40% of the C. coli isolates were resistant to ciprofloxacin (37). A second survey in Minnesota isolated Campylobacter from 88% of retail chicken meats purchased in 1997, including C. jejuni in 74% and C. coli in 21%. Ciprofloxacin-resistant Campylobacter was identified in 20% of retail chicken products (18). In this study, compar- ison of molecular subtypes from human and retail chicken quinolone-resistant C. jejuni isolates found that six of seven subtypes were indistinguishable from each other. In the United States, the FDA has approved the use of fluoroquinolones at different times for humans and food animals. Fluoroquinolones have been commonly used in humans for treating intestinal and other infections since 1986 (32). The first fluoroquinolones to be FDA-approved for use in food animals in the United States were sarafloxacin in 1995 and enrofloxacin in 1996. These flu- oroquinolones were approved for use in chickens and turkeys to treat bacterial respiratory infections principally caused by E. coli. These agents are typically administered to the entire poultry house (often >20,000 birds) through drinking water, which results in the treatment of sick and Antimicrobial-resistant Campylobacter healthy birds with various concentrations of fluoro- quinolones. The extent of fluoroquinolone use in chickens and turkeys in the United States is not known; manufactur- ers and farmers are not required to report these data. The Animal Health Institute has estimated that 1%–2% of the approximately 8 billion broiler chickens slaughtered each year in the United States are treated with fluoroquinolones (38). An experiment with Campylobacter-infected chick- ens treated with enrofloxacin and sarafloxacin showed that ciprofloxacin resistance rapidly developed among Campylobacter (39). An association between the approval of fluoro- quinolones for use in food-producing animals and the development of fluoroquinolone-resistant Campylobacter in animals and humans has been noted in several coun- tries. The approval of fluoroquinolones for use in food animals has been followed temporally by a rise in ciprofloxacin-resistant Campylobacter and other enteric pathogens isolated from animals and humans in Denmark, the Netherlands, and Spain (13,40). After the use of oral fluoroquinolones in pigs was discontinued in Denmark in 1999, nalidixic acid resistance among C. coli isolates from pigs decreased from 17% in 1998 to 5% in 2001 (41). In the United States, FDA has recently conducted a quantitative risk assessment and concluded that fluoro- quinolone use in chickens and turkeys results each year in >10,000 human infections with fluoroquinolone-resistant Campylobacter in persons who seek medical care and are treated with fluoroquinolones (42). FDA proposed the withdrawal of approval of fluoroquinolones for use in poultry in October 2000 (43). This is the first time a pro- posal has been made to withdraw an approval for an antimicrobial used in agriculture because of associated emergence of resistance in humans. The manufacturer of sarafloxacin has since withdrawn this product from the market, but the manufacturer of enrofloxacin continues to Figure 2. Quinolone- and fluoroquinolone-resistant Campylobacter jejuni in the United States, 1982–2001. FQ, fluoroquinolone; MN, Minnesota quinolone resistance among C. jejuni strains data (adapted from 18), NARMS, National Antimicrobial Resistance Monitoring System. Prior survey data adapted from reference 19 and 30. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004 1107