What is Helicobacter pylori (H. pylori)?

What is Helicobacter pylori (H. pylori)?

Helicobacter pylori is a gram-negative, microaerophilic, flagellated bacterium that colonizes the human stomach and is the most common chronic bacterial infection worldwide, affecting approximately 50% of the global population. 1, 2

Bacteriology and Epidemiology

• H. pylori is a spiral-shaped bacterium with flagella that normally resides on the luminal surface of gastric epithelial cells 3, 1
• The infection is acquired predominantly during childhood and persists chronically unless treated with specific eradication therapy 2, 4
• Prevalence varies widely by geographic region, socioeconomic status, and living conditions, with higher rates in developing countries where crowded conditions and poor sanitation facilitate person-to-person transmission 2, 4
• Transmission occurs primarily through oral-oral or fecal-oral routes between family members, with waterborne transmission also playing a role in areas with contaminated water supplies 2

Clinical Significance and Disease Associations

H. pylori infection is the most consistent risk factor for gastric cancer and represents a preventable cause of one of the most common fatal malignancies worldwide. 3

Major Gastric Conditions

• Chronic gastritis: H. pylori causes persistent inflammation of the gastric mucosa in all infected individuals 5, 6
• Peptic ulcer disease: The infection significantly increases risk of both gastric and duodenal ulcers 3, 7, 8
• Gastric cancer: H. pylori is classified as a Group 1 carcinogen, with infection leading to progression through chronic gastritis → atrophic gastritis → intestinal metaplasia → dysplasia → adenocarcinoma 3
• MALT lymphoma: Approximately 50% of gastrointestinal non-Hodgkin's lymphomas are low-grade gastric MALT lymphomas linked to H. pylori, and 60-80% can be cured by eradication alone in early stages 3

Interaction with Medications

• H. pylori increases risk of ulcers and bleeding in patients taking NSAIDs or low-dose aspirin 3
• Long-term PPI therapy in H. pylori-positive patients accelerates progression to corpus-predominant atrophic gastritis 3
• The infection impairs absorption of thyroxine and L-dopa through decreased acid secretion 3

Extragastric Manifestations

The Maastricht IV/Florence Consensus established strong evidence linking H. pylori to:

• Iron-deficiency anemia (Evidence level 1a, Grade A) 3, 6
• Idiopathic thrombocytopenic purpura (Evidence level 1b, Grade A) 3, 6
• Vitamin B12 deficiency (Evidence level 3b, Grade B) 3, 6

Key Clinical Distinctions

H. pylori infection differs fundamentally from acute gastroenteritis in that it causes chronic, persistent gastric inflammation rather than acute diarrheal illness. 5, 6

• H. pylori is not a primary cause of diarrhea; its main manifestations are upper gastrointestinal 6
• The infection progresses slowly over years to decades, leading to long-term complications like atrophic gastritis and cancer 5
• Treatment requires specific multi-antibiotic eradication regimens, not symptomatic management 5, 7

Diagnostic Approaches

H. pylori can be diagnosed through both invasive and non-invasive methods 3:

Invasive (requiring endoscopy):

• Histology with immunohistochemistry (gold standard, 90-95% sensitivity) 3
• Rapid urease test (80-95% sensitivity, requires ≥10⁴ organisms) 3

Non-invasive:

• Validated serological tests for H. pylori antibodies 3
• Urea breath tests 3
• Stool antigen tests 3

Critical Management Principles

Eradication of H. pylori is mandatory in patients with peptic ulcer history before starting NSAID treatment (Evidence level 1b, Grade A). 3

• The 2024 ACG guideline recommends 14-day bismuth quadruple therapy as preferred first-line treatment when antibiotic susceptibility is unknown 7
• H. pylori eradication is first-line treatment for low-grade gastric MALT lymphoma (Evidence level 1a, Grade A) 3
• Eradication reduces gastric cancer risk most effectively when performed before development of preneoplastic conditions like atrophic gastritis or intestinal metaplasia 3
• In populations at high risk for gastric cancer, H. pylori eradication strategies should be undertaken (Evidence level 1c, Grade A) 3

Common Clinical Pitfalls

• Failing to confirm eradication after treatment leads to persistent infection and continued complication risk 5
• Using clarithromycin or levofloxacin-based regimens in patients with prior macrolide or fluoroquinolone exposure results in treatment failure due to resistance 5, 7
• Not testing for H. pylori before starting aspirin in patients with peptic ulcer history increases bleeding risk 5
• Treating H. pylori solely to resolve diarrhea lacks evidence-based support, as diarrhea is not a primary manifestation of infection 6