RESEARCH white, 82 (26%) were black, 5 (2%) were Asian, 2 (0.6%) were Native American, and 4 (1%) were of other ethnic backgrounds. The most common endoscopic diagnoses for conditions of HARP participants were gastric erosions, gastritis, duodenal and gastric ulcers, and esophagitis (Table 1). H. pylori resistance was not statistically associ- ated with endoscopic findings. Among 347 H. pylori isolates submitted to HARP from 1998 to 2002, 118 (34%) were resistant to >1 antimicrobial agent, 101 (29%) H. pylori isolates were resistant to one agent only, and 17 (5%) H. pylori isolates were resistant to more than one antimicrobial agent. Three isolates were resistant to amoxicillin (1%), 45 were resistant to clar- ithromycin (13%), 87 were resistant to metronidazole (25%), and no isolate was found to be resistant to tetracy- cline. Multiple-agent resistance was observed for clar- ithromycin and amoxicillin (1 isolate, 0.3%) and clarithromycin and metronidazole (16 isolates, 5%). A test of trend showed no significant trend for resistance to metronidazole, but a significant trend (R2 = 0.76) was noted for a decline in resistance to clarithromycin during the study period (Figure). Most isolates were submitted by centers in the Northeast region, followed by the South, Midwest, and the West. Submitted H. pylori isolates from the Northeast region had the highest frequency of single- and dual-agent resistance (Table 2). The Midwest region submitted H. pylori isolates with the second-highest single agent resist- ance rate, while the southern region had the second-high- est dual agent resistance rate. The highest proportion of H. pylori isolates resistant to clarithromycin, metronidazole, and amoxicillin was in the Northeast (Table 2). The four sites reporting the highest proportion of iso- lates resistant to one agent were Indianapolis, Indiana; Galveston, Texas; Philadelphia, Pennsylvania; and Washington, DC (Table 3). Dual agent resistance was most prevalent in Detroit, Michigan. Indianapolis had the high- est overall resistance: 50% of all isolates submitted were resistant to at least one agent. The Atlanta site reported the highest proportion of clarithromycin-resistant isolates (Table 3). The highest proportion of metronidazole resist- ance was reported from the Indianapolis site. Isolates resistant to amoxicillin were found in Nashville, Tennessee, Philadelphia, and Washington, DC. Demographic, clinical, and epidemiologic data were analyzed for association with infection by a resistant H. pylori strain. Results of univariate analysis of risk factors for antimicrobial resistance are summarized in Table 4. On univariate analysis, significant risk factors for H. pylori resistance included past treatment of H. pylori infection with clarithromycin, treatment of past H. pylori infection for a second time in the past 5 years, treatment of past H. pylori infection with clarithromycin more than once, and Table 1. Endoscopy findings on patients enrolled in the Helicobacter pylori Antimicrobial Resistance Monitoring Project, 1998–2002a Endoscopic diagnosis No. of patients (%) Stomach erosion 88 (27.0) Gastritis 36 (11.0) Duodenal ulcers 26 (8.0) Esophagitis 26 (8.0) Gastric ulcer 26 (8.0) Duodenal erosion 24 (7.0) Barrett esophagus 9 (3.0) Nodularity 8 (2.0) Stomach tumor 4 (1.0) Bleedingb 1 (0.3) Other diagnosis 27 (8.0) aN = 331; H. pylori resistance is not associated with disease phenotype. bCause not specified. treatment of past H. pylori infection with a proton pump inhibitor more than once. No protective factors for resist- ant H. pylori resistance approached significance. On multivariate analysis, the most significant risk fac- tor for H. pylori resistance was previous treatment of H. pylori infection within the past 5 years (Table 5). Protective factors for H. pylori infection were treatment with an antacid (Mylanta) and submission of specimens from New York, Palo Alto, California, Atlanta, or Nashville. However, a high degree of colinearity was found between geographic location and race in this model. For example, 84% of Washington, DC, participants were black, compared to 20% of participants from Nashville. Accordingly, a second multivariate model was constructed in which geographic location was controlled by condition- ing. In this model, black race was the only risk factor sig- nificantly associated with infection with a resistant H. pylori strain (Table 6). Figure. Resistance of Helicobacter pylori isolates submitted to the Helicobacter pylori Antimicrobial Resistance Monitoring Project, 1998-2002 (N = 347).1998, n = 7 isolates; 1999, n = 137 isolates. Resistance to tetracycline was found in 0% of isolates during each year of the monitoring project. 1090 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004