What is Helicobacter pylori (H. pylori)?

What is Helicobacter pylori (H. pylori)?

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

Bacteriology and Epidemiology

• H. pylori is a spiral-shaped, gram-negative rod that normally resides in the gastric mucosa and possesses flagella that enable movement through the mucus layer 1, 2
• All fresh isolates express significant urease activity, which is essential for the bacterium's survival by neutralizing gastric acid and creating a more hospitable microenvironment 2
• The bacterium colonizes a unique biological niche within the gastric lumen, persisting despite the hostile acidic environment 2
• In developing countries, 70-90% of the population carries H. pylori, while prevalence is lower in developed nations 2
• There is no substantial reservoir of H. pylori aside from the human stomach 2
• Transmission occurs through iatrogenic, fecal-oral, and oral-oral routes, with person-to-person contact being the primary suspected mode 2, 3

Clinical Manifestations and Disease Associations

Primary Gastrointestinal Diseases

• H. pylori infection causes chronic gastritis in all infected individuals and is the most consistent risk factor for gastric cancer 4, 5
• The main clinical manifestations include chronic gastritis, peptic ulcer disease (both gastric and duodenal ulcers), gastric MALT lymphoma, and gastric adenocarcinoma 5, 6, 7
• Although most infected individuals never develop complications, significant mucosal inflammation can lead to peptic ulcers in the stomach and duodenum 1, 7
• H. pylori is recognized as a Class I carcinogen, with its elimination being the most promising strategy to reduce gastric cancer incidence 4

Disease Progression

• The infection causes chronic, persistent inflammation of the gastric mucosa that progresses slowly over time 6
• H. pylori gastritis can progress to atrophic gastritis, particularly in patients on long-term proton pump inhibitor (PPI) therapy (>1 year) 8, 6
• Atrophic gastritis may be reversible only in the corpus but not in the antrum, while intestinal metaplasia is considered irreversible 4
• The risk of gastric cancer can be reduced more effectively by employing eradication treatment before the development of preneoplastic conditions 4, 6

Extragastric Manifestations

• Iron-deficiency anemia is a confirmed extragastric manifestation with Grade A evidence for H. pylori testing and eradication 5
• Idiopathic thrombocytopenic purpura (ITP) is recognized as an extragastric manifestation with Evidence level 1b and Grade A recommendation 5
• Vitamin B12 deficiency is associated with H. pylori infection (Evidence level 3b, Grade B recommendation) 5
• H. pylori affects the bioavailability of certain medications including thyroxine and L-dopa 5
• The bacterium can affect organ systems outside the gastrointestinal tract, including the skin, liver, and heart 1
• H. pylori infection can adversely affect the nutritional status of both children and adults 1

Diagnosis

Invasive Tests (Requiring Endoscopy)

• Histological examination with immunohistochemistry is the established gold standard for histology, with sensitivity of 90-95% and specificity of 95-98% 4
• Modified Giemsa staining is the method of choice because it is sensitive, cheap, easy to perform, and reproducible 4
• At least two samples from the antrum and two from the body should be examined to improve sensitivity substantially 4
• Rapid urease test (RUT) has sensitivity of 80-95% and specificity of 95-100% in pretreatment settings, requiring 10⁴ organisms for a positive result 4
• Culture allows for antibiotic susceptibility testing, which is increasingly important given rising antibiotic resistance 4

Noninvasive Tests

• Breath tests (urea breath test) do not require endoscopy and are highly accurate 4, 2
• Serology (blood tests) can detect H. pylori antibodies but cannot distinguish active from past infection 4, 1
• Validated serological tests for H. pylori and markers of atrophy (pepsinogens) are the best available noninvasive tests to identify subjects at high risk of gastric cancer 4
• Stool antigen tests and urinary excretion of [15N]ammonia are additional noninvasive options 2

Treatment Principles

• In the face of increasing antibiotic resistance, current guidelines have coalesced around quadruple therapies for initial therapy, with 14-day bismuth quadruple therapy being the preferred first-line choice when susceptibility testing is not available 4, 9
• Successful eradication of H. pylori results in healing of gastritis without the need for long-term PPI therapy after confirmation of eradication 8, 6
• H. pylori requires specific eradication therapy with multiple antibiotics, distinguishing it from acute gastroenteritis which is self-limited 6
• Confirmation of eradication after treatment is mandatory to ensure persistent infection does not continue 6

Important Clinical Distinctions

• H. pylori is not associated with diarrhea as a primary manifestation; patients with diarrhea and H. pylori likely have another cause for their diarrhea 5
• The infection does not typically cause fever as a primary clinical manifestation, though advanced gastric cancer complications may cause fever 5
• H. pylori status does not affect the severity of symptoms, recurrence, or efficacy of treatment in gastroesophageal reflux disease (GERD) 8