Perhaps, hereditary or environmental factors yet to be discovered cause some individuals to develop problems. Alternatively, symptoms and ulcers may result from infection with more virulent strains of bacteria. These unanswered questions are the subject of intensive scientific research. Studies show that H. pylori infection in the United States varies with age, ethnic group, and socioeconomic class. The bacteria are more common in older adults, African Americans, Hispanics, and lower socio- economic groups.
Most individuals seem to be infected during childhood, and their infection lasts a lifetime.