least half the world's population was infected by the bacterium, making it the most widespread infection in the world. actual infection rates vary from nation to nation; the developing world has much higher infection rates than the developed one, notably western europe, north america, and australasia. the global prevalence of the bacterium declined markedly in the decade following 2010, with a particular reduction in africa. the age when someone acquires this bacterium seems to influence the pathologic outcome of the infection. people infected at an early age are likely to develop more intense inflammation that may be followed by atrophic gastritis with a higher subsequent risk of gastric ulcer, gastric cancer, or both. acquisition at an older age brings different gastric changes more likely to lead to duodenal ulcer. infections are usually acquired in early childhood in all countries. however, the infection rate of children in developing nations is higher than in industrialized nations, probably due to poor sanitary conditions, perhaps combined with lower antibiotics usage for unrelated pathologies. in developed nations, it is currently uncommon to find infected children, but the percentage of infected people increases with age, with about 50% infected for those over the age of 60 compared with around 10% between 18 and 30 years. the higher prevalence among the elderly reflects higher infection rates in the past when the individuals were children rather than more recent infection at a later age of the individual. in the united states, prevalence appears higher in african-american and hispanic populations, most likely due to socioeconomic factors. the lower rate of infection in the west is largely attributed to higher hygiene standards and widespread use of antibiotics. despite high rates of infection in certain areas of the world, the overall frequency of h. pylori infection is declining. however, antibiotic resistance is appearing in h. pylori; many metronidazole- and clarithromycin-resistant strains are found in most parts of the world. history