RESEARCH Antimicrobial Resistance among Campylobacter Strains, United States, 1997–2001 Amita Gupta,* Jennifer M. Nelson,* Timothy J. Barrett,* Robert V. Tauxe,* Shannon P. Rossiter,* Cindy R. Friedman,* Kevin W. Joyce,* Kirk E. Smith,† Timothy F. Jones,‡ Marguerite A. Hawkins,§ Beletshachew Shiferaw,¶ James L. Beebe,# Duc J. Vugia,** Terry Rabatsky-Ehr,†† James A. Benson,‡‡ Timothy P. Root,§§ and Frederick J. Angulo* for the NARMS Working Group We summarize antimicrobial resistance surveillance data in human and chicken isolates of Campylobacter. Isolates were from a sentinel county study from 1989 through 1990 and from nine state health departments par- ticipating in National Antimicrobial Resistance Monitoring System for enteric bacteria (NARMS) from 1997 through 2001. None of the 297 C. jejuni or C. coli isolates tested from 1989 through 1990 was ciprofloxacin-resistant. From 1997 through 2001, a total of 1,553 human Campylobacter isolates were characterized: 1,471 (95%) were C. jejuni, 63 (4%) were C. coli, and 19 (1%) were other Campylobacter species. The prevalence of ciprofloxacin-resistant Campylobacter was 13% (28 of 217) in 1997 and 19% (75 of 384) in 2001; erythromycin resistance was 2% (4 of 217) in 1997 and 2% (8 of 384) in 2001. Ciprofloxacin-resistant Campylobacter was isolated from 10% of 180 chicken products purchased from grocery stores in three states in 1999. Ciprofloxacin resistance has emerged among Campylobacter since 1990 and has increased in preva- lence since 1997. Cgastroenteritis in the United States, causing an esti- ampylobacter is the most common cause of bacterial mated 2.4 million human infections annually (1). Diagnosed infections have declined in recent years. In *Centers for Disease Control and Prevention, Atlanta, Georgia, USA, †Minnesota Department of Health, Minneapolis, Minnesota, USA; ‡Tennessee Department of Health, Nashville, Tennessee, USA; §Maryland Department of Health and Mental Hygiene, Baltimore, Maryland, USA; ¶Oregon Department of Human Services, Portland, Oregon, USA; #Colorado Department of Public Health & Environment, Denver, Colorado, USA; **California Department of Health Services, Berkeley, California, USA; ††Connecticut Department of Public Health, Hartford, Connecticut, USA; ‡‡Georgia Department of Human Services, Atlanta, Georgia, USA; and §§New York State Department of Health, Albany, New York, USA 2001, FoodNet surveillance identified 13.4 diagnosed Campylobacter infections per 100,000 persons (2). Approximately 95% of diagnosed Campylobacter infec- tions are due to C. jejuni (3). Although most Campylo- bacter infections cause an acute, self-limited illness charac- terized by diarrhea, fever, and abdominal cramps, severe infections do occur (4). Antimicrobial treatment can short- en the duration of illness and may be life-saving in invasive infections (5–7). Fluoroquinolones (e.g., ciprofloxacin) are often prescribed empirically for the treatment of gastroen- teritis and for Campylobacter infections in adults (6,8). Quinolones (e.g., nalidixic acid), although now seldom used for treatment in the United States, are frequently used to screen for fluoroquinolone resistance because of the close correlation between quinolone and fluoroquinolone resistance among Campylobacter. Macrolides, such as erythromycin, are also prescribed to treat Campylobacter infections (4,9). Fluoroquinolone-resistant Campylobacter infections in humans were first detected in Europe in the late 1980s (10–12). Subsequently, an increasing proportion of Campylobacter isolates around the world have been found to be fluoroquinolone-resistant (13). Studies in the United States, Europe, and New Zealand have identified poultry as a principal source of Campylobacter infection (14–16). Quinolones have been available in human medicine since the mid-1960s, and the first fluoroquinolone (ciprofloxacin) was approved for use in humans in 1986. Two fluoroquinolones, sarafloxacin and enrofloxacin, were approved for use in poultry by the U.S. Food and Drug Administration (FDA) in 1995 and 1996, respective- ly (17). These fluoroquinolones were the first ones approved in food animals; subsequently, other fluoro- quinolones have been approved for veterinary use but not for use in poultry (18). 1102 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004