RESEARCH the 7 days before illness onset) with a standardized ques- tionnaire. 1999 Retail Survey Three NARMS-participating state health departments (Georgia, Maryland, and Minnesota) participated in a sur- vey of retail chicken products. From January to June 1999, each site purchased a convenience sample of 10 whole broiler chickens per month from supermarkets located within the state. State public health laboratories at each site tested the samples for Campylobacter. Carcass rinse sam- ples were centrifuged, and pellets were incubated in enrichment broth and plated onto Campylobacter blood agar plates according to methods published elsewhere (27); neither media contained quinolone or macrolide antimicrobial agents. Campylobacter isolates were for- warded to CDC for species identification and antimicro- bial susceptibility testing according to NARMS methods. Results National Surveillance 1989–1990 Sentinel County Study Two hundred ninety-eight patients were interviewed, and their Campylobacter isolates were tested. Of these iso- lates, 289 (97%) were C. jejuni, 8 (3%) were C. coli, and 1 (0.3%) was a C. lari. None were resistant to ciprofloxacin, and 3 (1%) of 294 were resistant to nalidixic acid (MIC > 32 µ g/mL); 1 isolate was C. lari, which is inherently resist- ant to nalidixic acid (28), and 2 were C. jejuni. The C. lari isolate was resistant to ofloxacin (MIC = 8 µ g/mL), inter- mediately resistant to norfloxacin (MIC = 8 µ g/mL) but susceptible to ciprofloxacin (MIC = 2 µ g/mL).1 The two nalidixic acid-resistant C. jejuni isolates were susceptible to ciprofloxacin (MIC = 0.5 µ g/mL) and norfloxacin and ofloxacin (MIC < 2 µ g/mL). The proportion of the isolates resistant to tetracycline was 42% (124/295). The resistant proportion for the other antimicrobial agents tested were as follows: erythromycin 3% (8/295), clindamycin 2% (6/295), azithromycin 2% (5/294), chloramphenicol 0% (0/295), and gentamicin 0% (0/295). Travel history was available for 296 patients with Campylobacter infection; 23 (8%) patients traveled outside of the United States in the week before illness onset. Of the persons with avail- able information, 32 (11%) of 295 had taken an antimicro- bial agent in the 30 days before illness onset, 46 (15%) of 298 were hospitalized, and 241 (81%) of 297 were treated with an antimicrobial agent for their illness. Among the 234 persons for whom treatment data were available, the most common agents used for treatment were erythromy- cin (62%), ciprofloxacin (19%), and trimethoprim-sul- famethoxazole (5%). Of the three patients with nalidixic acid-resistant infections, none traveled outside the United States, and none were treated with a quinolone or fluoro- quinolone in the month before illness. NARMS, 1997–2001 From 1997 to 2001, a total of 1,932 presumptive Campylobacter isolates were received at CDC through NARMS; 193 (10%) were excluded because they were not viable, 104 (5%) were not in accordance with the one-a- week sampling method, 39 (2%) were determined not to be Campylobacter, 22 (1%) were duplicates, and 21 (1%) were contaminated cultures. Of the 1,553 (80%) isolates further characterized and included in this analysis, 1,471 (95%) were C. jejuni, 63 (4%) were C. coli, 7 (0.4%) were C. upsaliensis, 5 (0.3%) were C. fetus, 2 (0.1%) were C. lari, and 5 (0.3%) were undetermined (i.e., determination by 16S study did not identify a species). Forty-five percent of case-patients were female; the median age was 33 years (range <1–96). Among 1,439 isolates with known source of specimen collection, 1,426 (99%) were from stool sam- ples, and 13 (1%) were from blood samples. Among blood isolates, eight were C. jejuni, two were C. fetus, two were C. upsaliensis, and one was C. lari. The results of susceptibility testing among Campylobacter isolates by species are shown in Table 1. Resistance to ciprofloxacin among all Campylobacter iso- lates was 13% in 1997 and 19% in 2001. Resistance to erythromycin among all Campylobacter isolates was 2% in 1997 and 2% in 2001. The results of antimicrobial sus- ceptibility testing by year for isolates of the most common species, C. jejuni, are shown in Table 2 The prevalence of ciprofloxacin-resistant Campylo- bacter ranged from 0% (0/14) in Tennessee in 1999 to 26% (14/53) in Georgia in 2001. By using a multivariate logis- tic regression model and controlling for age and site-to-site variation in prevalence, the proportion of all Campylobacter isolates resistant to ciprofloxacin and nalidixic acid in 2001 was significantly higher than the proportion of isolates resistant to ciprofloxacin in 1997 (data only shown for ciprofloxacin in Table 3). The remaining antimicrobial drugs had no statistically signifi- cant change in resistance over time (data not shown). Fifty-one percent of Campylobacter isolates were resistant to >1 drug, 18% were resistant to >2 drugs, and 10% were resistant to >3 drugs. The most common mul- tidrug resistance (i.e., >2 drugs) pattern included ciprofloxacin, nalidixic acid, and tetracycline. 1This isolate was reported to be ciprofloxacin resistant in reference 20; more recently established interpretive criteria define it as sus- ceptible. 1104 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004