A 62-year-old man presents to the emergency department with a 1-day history of dark tarry stools and light-headedness. He also reports a 1-month history of intermittent abdominal discomfort and poor appetite. For the pain he takes ibuprofen on an as needed basis.On physical examination, the blood pressure is 102/75mm Hg, heart rate is 110/min, and the abdomen is soft and nontender. He undergoes urgent upper endoscopy that finds an ulcerating lesion in his stomach and biopsies confirm gastric cancer. Which of the following is a risk factor for carcinoma of the stomach?