Helicobacter pylori (H. pylori), formerly known as Campylobacter pylori, is a highly mobile spiral-shaped gram-negative bacterium with a cilium at one pole. It is the most common infection due to bacteria. It is estimated that 50% of the global population is infected with a great geographical disparity, reaching up to 80% in poor and developing countries, compared to an incidence of 20–50% in developed countries.

Another meta-analysis debated the 2015 regional prevalence of the infection and found that 4.4 billion people worldwide had H. pylori infection. The highest prevalence was in Africa, with a percentage of 70.1%. 

The special helical shape of the bacteria is useful to penetrate and causes an inflammatory reaction of the gastric mucosa with humoral and tissue immune reactions. Gastritis may remain stable or may progress to ulcer, mucosal atrophy, or may progress to two malignancies: adenocarcinoma and gastric mucosa-associated lymphoid tissue (MALT) lymphoma. There is a direct correlation between the presence of H. pylori infection and gastroduodenal ulcers, with over 90% of people being infected with H. pylori. According to the World Health Organization (WHO), H. pylori infection contributes to approximately 75% of stomach cancers and 5.5% of all cancers.