RESEARCH Antimicrobial Resistance Incidence and Risk Factors among Helicobacter pylori–Infected Persons, United States William M. Duck,* Jeremy Sobel,* Janet M. Pruckler,* Qunsheng Song,* David Swerdlow,* Cindy Friedman,* Alana Sulka,* Balasubra Swaminathan,* Tom Taylor,* Mike Hoekstra,* Patricia Griffin,* Duane Smoot,† Rick Peek,‡ DavidC. Metz,§ Peter B. Bloom,¶ Steven Goldschmid,¶ Julie Parsonnet,# George Triadafilopoulos,# Guillermo I. Perez-Perez,** Nimish Vakil,†† Peter Ernst,‡‡ Steve Czinn,§§ Donald Dunne,¶¶ and Ben D. Gold* Helicobacter pylori is the primary cause of peptic ulcer disease and an etiologic agent in the development of gas- tric cancer. H. pylori infection is curable with regimens of multiple antimicrobial agents, and antimicrobial resistance is a leading cause of treatment failure. The Helicobacter pylori Antimicrobial Resistance Monitoring Program (HARP) is a prospective, multicenter U.S. network that tracks national incidence rates of H. pylori antimicrobial resistance. Of 347 clinical H. pylori isolates collected from December 1998 through 2002, 101 (29.1%) were resistant to one antimicrobial agent, and 17 (5%) were resistant to two or more antimicrobial agents. Eighty-seven (25.1%) isolates were resistant to metronidazole, 45 (12.9%) to clar- ithromycin, and 3 (0.9%) to amoxicillin. On multivariate analysis, black race was the only significant risk factor (p < 0.01, hazard ratio 2.04) for infection with a resistant H. pylori strain. Formulating pretreatment screening strategies or providing alternative therapeutic regimens for high-risk populations may be important for future clinical practice. Twide is approximately 50% (1), as high as 80%–90% he prevalence of Helicobacter pylori infection world- in developing countries, and ≈35%–40% in the United *Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †Howard University Medical Center, Washington, DC, USA; ‡Vanderbilt University Medical Center, Nashville, Tennessee, USA; §University of Pennsylvania Medical Center, Philadelphia, Pennsylvania, USA; ¶Atlanta Veterans Affairs Medical Center, Atlanta, Georgia, USA; #Stanford University Medical Center, Palo Alto, California, USA; **New York University School of Medicine, New York, New York, USA; ††Sinai Samaritan Medical Center, Milwaukee, Wisconsin, USA; ‡‡University of Virginia, Charlottesville, Virginia, USA; §§University Hospitals of Cleveland, Cleveland, Ohio, USA; and ¶¶Indiana University Medical Center, Indianapolis, Indiana, USA States (1). Approximately 20% of persons infected with H. pylori develop related gastroduodenal disorders during their lifetime (1). H. pylori is an etiologic agent of peptic ulcer disease, primary gastritis, gastric mucosa-associated lymphoid-tissue lymphoma, and gastric adenocarcinoma (2). The annual incidence of H. pylori infection is ≈4%–15% in developing countries, compared with approximately 0.5% in industrialized countries (3). Documented risk factors include low socioeconomic sta- tus, overcrowding, poor sanitation or hygiene, and living in a developing country (2). Eradication therapy of symptomatic H. pylori infection substantially reduces the recurrence of associated gastro- duodenal diseases. Therapy entails complicated regimens of several antimicrobial agents for at least 2 weeks. In gen- eral, triple therapy regimens usually entail two of the fol- lowing antimicrobial agents: metronidazole, amoxicillin, tetracycline, or clarithromycin in combination with a pro- ton pump inhibitor or bismuth (4). The most common causes of treatment failure are patient noncompliance and antimicrobial resistance of the infecting H. pylori strain (5). Quadruple regimens are used as a salvage therapy when triple therapy regimens have failed (4). Pretreatment resistance of H. pylori has been reported to compromise the efficacy of treatment. For example, therapy regimens containing metronidazole and clarithromycin fail in as many as 38% and 55% of cases, respectively, when used to treat infection with an organism resistant to one of these antimicrobial agents (6). In addition, published data are lacking that describe the effect conferred by polymicrobial resistance on eradication success. The Helicobacter pylori Antimicrobial Resistance Monitoring Project (HARP) is a prospective, longitudinal 1088 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 6, June 2004