Helicobacter pylori Infection

Helicobacter pylori is a spiral, microaerophilic bacterium that colonises the gastric mucosa, where it causes chronic gastritis and is a major cause of peptic ulcer disease. Long-standing infection is also an established risk factor for gastric cancer, and the organism's discovery reshaped the understanding of upper gastrointestinal disease.

Definition

Helicobacter pylori infection is colonisation of the gastric mucosa by the bacterium H. pylori, which induces chronic active gastritis and is causally associated with peptic ulcer disease and an increased risk of gastric cancer.

Scope

This entry covers H. pylori infection as a clinical entity: the organism, its colonisation of the stomach, the chronic gastritis it produces, its links to peptic ulcer disease and gastric malignancy, epidemiology, and the evidence summarised in consensus reports. It is a reference overview and does not give individualised diagnostic or eradication treatment advice.

Core questions

• How does H. pylori survive in the acidic stomach and establish chronic colonisation?
• Why does the same infection lead to ulcers in some people and gastric cancer in others?
• How did the discovery of H. pylori change the understanding of peptic ulcer disease?

Key concepts

• Gastric colonisation and chronic active gastritis
• Urease and acid adaptation
• Virulence factors (e.g., CagA, VacA)
• Peptic ulcer disease
• Gastric cancer and MALT lymphoma risk
• Faecal-oral and oral-oral transmission
• Non-invasive testing (urea breath test, stool antigen)

Mechanisms

Helicobacter pylori survives the gastric environment by producing urease, which generates ammonia to buffer local acidity, and by using its flagella and spiral shape to penetrate the mucus layer and adhere to the epithelium. Persistent colonisation provokes a chronic inflammatory response (chronic active gastritis). Strain virulence factors such as the cytotoxin-associated gene A (CagA) and the vacuolating cytotoxin (VacA) influence the intensity of injury and the likelihood of progression. Depending on the pattern and distribution of gastritis and host and environmental factors, infection can favour duodenal or gastric ulceration, or, over long periods, the atrophic and metaplastic changes that increase gastric cancer risk.

Clinical relevance

H. pylori is the principal infectious cause of peptic ulcer disease and a recognised carcinogen for gastric adenocarcinoma and MALT lymphoma. Recognising it as an infection rather than a purely acid-related disorder reframed the evaluation of dyspepsia and ulcers. This entry describes the infection for reference and is not a basis for individual testing or eradication therapy decisions.

Epidemiology

A systematic review and meta-analysis estimated that roughly half of the world's population is infected with H. pylori, with higher prevalence in many low- and middle-income regions and a declining trend in some high-income settings (Hooi et al., 2017). Infection is usually acquired in childhood and persists for life unless treated.

Evidence & guidelines

Consensus reports including the Kyoto global consensus on H. pylori gastritis (Sugano et al., 2015) and the Maastricht VI/Florence consensus (Malfertheiner et al., 2022) summarise the diagnosis and management framework, and the foundational observation was reported by Marshall and Warren (1984). This entry conveys orientation, not prescriptive care.

History

Curved bacteria had been seen in the stomach by earlier observers, but Barry Marshall and Robin Warren's 1984 report linking the organism to gastritis and peptic ulceration overturned the prevailing view that the stomach was sterile and that ulcers were primarily due to acid and stress. Their work, recognised with a Nobel Prize, established H. pylori as an infectious cause of upper gastrointestinal disease and reframed its treatment around eradication.

Debates

Should H. pylori be treated in all infected people to prevent gastric cancer?

Consensus reports increasingly frame H. pylori gastritis as an infectious disease warranting eradication, but the balance of population-wide screen-and-treat against antibiotic resistance, reinfection, and resource considerations remains debated.

Key figures

• Barry Marshall
• Robin Warren

Seminal works

• marshall-warren-1984
• hooi-2017

Frequently asked questions

How does H. pylori survive in stomach acid?

It produces the enzyme urease, which generates ammonia to neutralise acid locally, and it burrows into the protective mucus layer over the gastric epithelium, allowing it to persist in an otherwise hostile environment.

Does everyone with H. pylori develop ulcers or cancer?

No; most infected people remain asymptomatic, and only a minority develop peptic ulcers or gastric cancer, with risk shaped by bacterial strain, host, and environmental factors. This entry is educational and not a substitute for clinical evaluation.