H. pylori is a bacteria that can cause peptic ulcer disease and gastritis. (pain and inflammation of the stomach). Only 20% of those infected with the bacteria have symptoms. But for those who have symptoms, they include: Dull or burning stomach pain, weight loss, nausea, persistent burping or vomiting after meals. If left untreated, the H. Pylori bacteria may cause stomach ulcers and, long term, cancer.