Helicobacter pylori Infection

• Bacterial Colonization and Adherence: H. pylori survives the acidic gastric environment through robust urease enzyme expression, which hydrolyzes urea to ammonia and carbon dioxide, creating a microenvironment with pH 6-7 surrounding the bacterium and permitting survival despite ambient pH <3.5. The organism uses flagella to achieve motility through viscous mucus and expresses adhesins including blood group antigen-binding adhesin (BabA), which binds Lewis b antigen on gastric epithelial cells, and sialic acid-binding adhesin (SabA), which binds sialylated glycoproteins. These adhesion mechanisms enable intimate bacterial-epithelial contact and persistent colonization, distinguishing H. pylori from other gastric bacteria.

• Virulence Factor Expression and Host Cell Damage: The cagA (cytotoxin-associated gene A) encodes a 120 kDa protein that is injected into host epithelial cells via a type IV secretion system (encoded by the cag pathogenicity island), where it is phosphorylated by Src kinase and interacts with SHP-2 phosphatase, disrupting cell-cell junctions, increasing epithelial permeability, and promoting inflammatory cytokine secretion (IL-8, TNF-α). The vacA (vacuolating cytotoxin A) gene encodes a toxin forming anion-selective channels in mitochondrial membranes, inducing epithelial cell apoptosis and vacuolization; cagA and vacA polymorphisms (s1/s2, m1/m2, i1/i2 for vacA; cagA present/absent status) correlate with disease severity, with cagA+ s1m1 vacA strains associated with increased ulcer and cancer risk. Lipopolysaccharide (LPS) with unusual O-antigen structures that mimic Lewis antigen glycans on host mucosa enable molecular mimicry, allowing immune evasion while paradoxically triggering autoreactive responses.

• Inflammatory Response and Progressive Mucosal Damage: H. pylori infection triggers a robust innate and adaptive immune response characterized by recruitment of neutrophils, macrophages, and lymphocytes to the gastric mucosa through chemokine (IL-8, CXCL1) and toll-like receptor (TLR2, TLR4, TLR5) signaling. This chronic inflammation progresses through a histologically defined cascade: chronic active gastritis (initial phase with neutrophilic infiltration and lymphoid aggregates) → atrophic gastritis (loss of acid-secreting parietal cells and chief cells, metaplasia of gastric mucosa to intestinal-type epithelium) → intestinal metaplasia → dysplasia → gastric adenocarcinoma. The progressive atrophy reduces gastric acid production, permitting bacterial migration toward the gastric cardia and fundus, and creating a hypochlorhydric environment conducive to MALT lymphoma development. Pro-inflammatory Th1 and Th17 responses predominate, but H. pylori-specific regulatory T cells (Tregs) also expand, contributing to chronic persistent infection despite immune activation.

• Duodenal Ulcer Pathogenesis and Acid Hypersecretion: In duodenal ulcer formation (most common H. pylori-associated ulcer type), H. pylori causes gastritis predominantly affecting the fundus while sparing the antrum initially, maintaining normal or increased antral G-cell populations. Gastrin secretion from antral G-cells increases in response to reduced acid and inflammatory mediators (gastrin-releasing peptide), leading to elevated fasting serum gastrin levels (hypergastrinemia) and increased parietal cell acid secretion, which overwhelms duodenal bicarbonate buffering capacity and causes ulceration in the duodenum's first portion where gastric acid pH is highest. This contrasts with gastric ulcers (typically antral), which result from local mucosal damage without systemic acid hypersecretion.

• MALT Lymphoma Development: Prolonged H. pylori infection can drive clonal expansion of gastric mucosa-associated lymphoid tissue, initially antigen-dependent but potentially progressing to antigen-independent lymphoma in a subset of patients. The organism stimulates T-cell dependent B-cell proliferation, and in genetically predisposed individuals or with particular bacterial strains, malignant transformation of B-cells (usually CD5-negative marginal zone lymphoma) may occur; notably, eradication of H. pylori causes MALT lymphoma regression in ~70-80% of early-stage cases due to removal of the antigenic stimulus.

• Evasion of Gastric Defenses: H. pylori avoids clearance through multiple mechanisms: expression of superoxide dismutase and catalase to neutralize reactive oxygen species from neutrophils, secretion of phospholipase A2 and protease to degrade mucins, antigenic variation of surface proteins to evade antibody responses, and impairment of protective IgA responses despite strong IgG responses, creating a paradox of immune activation without pathogen clearance.

• Fecal-Oral and Oral-Oral Transmission: The primary route of acquisition is consumption of contaminated food or water, with highest incidence in childhood in endemic populations; crowded living conditions, poor sanitation, and low socioeconomic status dramatically increase transmission risk. Oral-oral transmission may occur through saliva, vomitus, or fecal contamination of hands, explaining clustering in families and between sexual partners. Healthcare workers have no significantly elevated risk, indicating low inoculum infectivity and need for prolonged contact.

• Demographic and Socioeconomic Risk Factors: Birth in or residence in developing countries (particularly Latin America, Africa, Middle East, Asia) carries substantially elevated risk; migration from endemic to non-endemic areas typically preserves infection status from childhood acquisition. Age of acquisition correlates inversely with current incidence in the country of residence—older individuals in developed countries more commonly infected due to higher historical prevalence during their childhood. Race/ethnicity associations reflect geographic origin rather than intrinsic susceptibility (African American and Hispanic individuals in the U.S. have higher prevalence reflecting ancestry). Male gender shows slight male predominance in some studies.

• Host Genetic Factors: Although H. pylori genotype drives virulence, human genetic polymorphisms in IL-1β (Pro12) and IL-1RN (interleukin-1 receptor antagonist) promoter regions increase susceptibility to severe gastritis and gastric cancer in some populations through enhanced pro-inflammatory responses. TNF-α and IL-10 polymorphisms modulate immune response intensity but are not absolute determinants of infection risk.

• Facilitating Factors for Persistence: Achlorhydria or hypochlorhydria from autoimmune gastritis or previous gastric surgery increases susceptibility to acquisition and persistence. Immunocompromise (HIV/AIDS with CD4 <200 cells/μL, transplant recipients) may alter infection manifestations and clearance.

• Acute H. pylori Infection (Rare presentation): Acute presentation occurs in only 5-10% of newly infected individuals and manifests with acute-onset epigastric pain, nausea, vomiting, and upper abdominal bloating lasting days to weeks, with acute inflammatory gastritis on endoscopy. Achlorhydria or hypochlorhydria may be present acutely due to inflammatory suppression of acid secretion before chronic changes develop. Most acute infections resolve spontaneously or progress silently to chronic colonization.

• Chronic Active Gastritis—Asymptomatic or Nonspecific Dyspepsia: The majority of chronically infected patients (70-80%) remain completely asymptomatic or report vague dyspeptic symptoms including postprandial fullness, early satiety, epigastric discomfort, bloating, and nausea without ulceration. Symptoms result from inflammatory damage reducing accommodation and secretory function rather than from acid hypersecretion. Absence of alarm features (weight loss, persistent vomiting, dysphagia, hematemesis) typically characterizes functional dyspepsia associated with H. pylori.

• Peptic Ulcer Disease—Symptomatic Presentations:
• Duodenal ulcer (most common ulcer type, affects ~15-20% of H. pylori-infected individuals) presents with epigastric pain characteristically occurring 2-3 hours after eating or at night, relieved by food or antacids initially before pain recurs ("food-induced pain" pattern). Acid hypersecretion secondary to elevated gastrin creates strongly acidic duodenal environment promoting ulceration at the duodenum's first portion.
• Gastric ulcer (antral predominance) may present similarly but tends to occur with meals rather than relief from food. Gastric ulcers carry higher bleeding risk and malignancy risk (ruling out gastric cancer is mandatory).
• Refractory or complicated ulcers present with hemorrhage (hematemesis, melena, iron-deficiency anemia with occult GI bleeding), perforation (acute severe epigastric pain with peritoneal signs, pneumoperitoneum), or penetration (severe boring epigastric pain radiating to back with nausea).

• MALT Lymphoma Presentations: Patients may present incidentally with gastric MALT lymphoma discovered during endoscopy for dyspepsia, or with B symptoms (fever, night sweats, weight loss) in advanced disease, or abdominal pain from gastric involvement. Approximately 90% of gastric MALT lymphomas are H. pylori-associated.

• Gastric Adenocarcinoma—Late Presentation: Patients with longstanding chronic atrophic gastritis and intestinal metaplasia may eventually develop gastric cancer, typically presenting in advanced stages with weight loss, persistent vomiting, dysphagia, early satiety, or upper GI hemorrhage. The progression from infection to cancer spans decades, with highest risk in individuals infected in childhood with virulent strains (cagA+ s1m1 vacA).

• Functional Dyspepsia Without Ulceration: Postprandial distress syndrome and epigastric pain syndrome occur in a subset of H. pylori-infected patients without endoscopic ulceration, attributed to inflammatory changes reducing accommodation and gastric motor function. Eradication may provide symptom relief in a minority of dyspeptic patients.

• Physical Examination Findings: Routine abdominal examination is typically unremarkable in uncomplicated infection; acute gastritis may reveal epigastric tenderness. Complicated ulcers present with peritoneal signs (rebound, guarding, rigidity) in perforation, or signs of hemorrhage (tachycardia, hypotension, pallor, melena). Advanced gastric cancer manifests with Virchow's node (left supraclavicular lymphadenopathy), Sister Mary Joseph's node (periumbilical nodule), or linitis plastica presentation.

• Clinical Variants and Syndromes:
• Achlorhydria syndrome: H. pylori infection causing severe fundic atrophy with loss of parietal cells, resulting in absent acid and elevated gastrin with MALT lymphoma risk
• Zollinger-Ellison-like syndrome: Rarely, severe H. pylori fundic gastritis mimics ZES with marked hypergastrinemia
• Post-gastrectomy H. pylori: Altered bacterial distribution and acid environment after gastric surgery affect infection presentation

• Clinical Approach and Test Selection:
• Noninvasive testing is preferred for initial diagnosis in patients without alarm features or prior endoscopy
• Invasive testing with endoscopy is indicated for patients with alarm features (age >60, weight loss, persistent vomiting, dysphagia, hematemesis, anemia, family history gastric cancer) to exclude malignancy
• Post-treatment confirmation requires testing ≥4 weeks after completion of eradication therapy to avoid false negatives from suppressed colonization

• Serology (Anti-H. pylori Antibodies):
• IgG antibodies remain positive for years after infection or successful eradication, making serology useful for epidemiologic surveys and identifying past infection but unreliable for current infection status
• Sensitivity 85-95% and specificity 79-98% depending on assay and population
• Cannot differentiate active from past infection
• False negatives occur in early infection (<2 weeks) before seroconversion and in severe atrophic gastritis with achlorhydria
• Utility: initial screening in antibody-negative populations; positive result warrants confirmatory noninvasive testing

• Urea Breath Test (UBT)—Gold Standard Noninvasive Test:
• Patient ingests 13C-labeled or 14C-labeled urea; if H. pylori present, bacterial urease cleaves urea to ammonia and labeled CO2, which is absorbed and exhaled
• Collected breath samples measured for labeled carbon ratio (delta over baseline)
• Sensitivity 95-98% and specificity 95-99%—highest among noninvasive tests
• Must discontinue PPIs ≥2 weeks and antibiotics ≥4 weeks before testing to avoid false negatives
• Preferred for post-treatment confirmation given high accuracy
• Disadvantage: cost, limited availability, cannot identify antibiotic resistance

• Stool Antigen Testing:
• Detects H. pylori antigen in feces using monoclonal or polyclonal antibodies (ELISA)
• Sensitivity 94-97% and specificity 93-98%
• Convenient, noninvasive, inexpensive
• May have reduced sensitivity in diarrhea or with concurrent antimotility agents
• Affected by timing relative to PPI/antibiotic use (discontinue ≥2 weeks and ≥4 weeks respectively)
• Acceptable for initial diagnosis and post-treatment confirmation; widely used due to accessibility

• Rapid Urease Test (During Endoscopy):
• Antral biopsy specimen placed in urea substrate medium; urease enzyme produced by H. pylori generates ammonia, changing pH indicator color within 1-24 hours
• Sensitivity 85-95% and specificity 95-100%; dependent on bacterial load (false negatives if low colonization) and prior antibiotic use
• Advantage: results within 24 hours, simultaneous endoscopic assessment for ulcers/malignancy
• Disadvantage: requires endoscopy; less sensitive than UBT in post-treatment assessment

• Histology and Culture:
• Multiple gastric biopsies (antrum, body, fundus) stained with H&E, Giemsa, or immunohistochemistry; identifies organism and assesses degree of gastritis (chronic active, atrophy, metaplasia, dysplasia)
• Sensitivity 93-98% and specificity 99% when multiple sites sampled
• Culture performed on biopsy specimens

Stabilize first if the ulcer has declared itself

• Acute upper GI bleed: two large-bore IVs, restrictive transfusion (hemoglobin threshold ~7 g/dL in hemodynamically stable patients), high-dose IV proton pump inhibitor (pantoprazole) to raise intragastric pH and stabilize clot, and upper endoscopy with hemostasis within 24 hours (ACG guideline on upper GI bleeding). Perforation with free air is a surgical emergency — omental (Graham) patch repair.
• Eradication therapy is started after stabilization; acute bleeding and PPI use both cause false-negative urease-based testing, so a negative test in that setting must be repeated later.

First-line eradication (ACG Clinical Guideline on treatment of H. pylori)

• Bismuth quadruple therapy, 14 days: PPI + bismuth subsalicylate + tetracycline + metronidazole. Preferred in the US because clarithromycin resistance now commonly exceeds the 15% threshold, and it is the regimen of choice for any patient with prior macrolide exposure or penicillin allergy.
• Clarithromycin triple therapy (PPI + clarithromycin + amoxicillin, 14 days): acceptable only where local clarithromycin resistance is known to be low and the patient is macrolide-naïve.
• Potassium-competitive acid blocker regimens: vonoprazan with amoxicillin ± clarithromycin is FDA-approved and provides more profound, sustained acid suppression than PPIs, improving antibiotic stability.
• Rifabutin triple therapy (omeprazole + amoxicillin + rifabutin) is an FDA-approved alternative with low resistance rates.

Salvage after failure

• Never reuse clarithromycin or levofloxacin if the first regimen contained it. Options include bismuth quadruple (if not already used), levofloxacin triple therapy, or rifabutin-based therapy. Susceptibility testing (culture or molecular) should be pursued when available — ideally after the first failure and certainly before a third regimen.

Confirm cure and definitive steps

• Test of cure in all treated patients ≥4 weeks after therapy with urea breath test or stool antigen, holding the PPI ≥2 weeks (antibiotics and bismuth ≥4 weeks). Serology cannot confirm eradication.
• Gastric ulcers require biopsy and endoscopic follow-up to exclude malignancy; early-stage MALT lymphoma is treated with eradication alone.

Contraindicated/avoid

• Tetracycline and bismuth in pregnancy and young children (tooth staining; Reye syndrome risk with salicylate); metronidazole with alcohol (disulfiram-like reaction); clarithromycin with QT-prolonging drugs and CYP3A4 substrates; amoxicillin in true penicillin allergy.

Complications of infection

• Upper GI hemorrhage (emergency): ulcer erosion into a submucosal vessel — classically the gastroduodenal artery in a posterior duodenal ulcer. Signals: hematemesis, melena, tachycardia/hypotension, falling hemoglobin.
• Perforation (emergency): full-thickness erosion, typically an anterior duodenal ulcer, spilling gastric contents. Signals: sudden severe epigastric pain, rigid abdomen, absent bowel sounds, free air under the diaphragm on upright film or CT.
• Penetration: posterior ulcer burrowing into pancreas — boring pain radiating to the back with elevated lipase.
• Gastric outlet obstruction: scarring/edema of the pylorus or duodenal bulb. Signals: nonbilious vomiting of undigested food, succussion splash, hypochloremic hypokalemic metabolic alkalosis.
• Gastric adenocarcinoma (intestinal type): chronic atrophic gastritis → intestinal metaplasia → dysplasia. Signals: weight loss, early satiety, iron-deficiency anemia, Virchow node.
• Gastric MALT lymphoma: chronic antigen-driven B-cell proliferation; often regresses with eradication, but t(11;18) predicts failure to respond.
• Extragastric associations: unexplained iron-deficiency anemia and adult immune thrombocytopenic purpura are ACG testing indications — test for and eradicate H. pylori in these patients (alongside active or past PUD, low-grade gastric MALT lymphoma, and history of endoscopic resection of early gastric cancer). Vitamin B12 deficiency is cited as an association in the Maastricht/Florence consensus only — weaker evidence, and not an ACG testing indication.

Complications of therapy

• Clostridioides difficile colitis (potentially emergent if toxic megacolon): antibiotic disruption of colonic flora — watery diarrhea, leukocytosis, positive stool toxin/PCR.
• Metronidazole: disulfiram-like reaction with alcohol, metallic taste, peripheral neuropathy with prolonged use.
• Clarithromycin: QT prolongation, altered taste, numerous CYP3A4 interactions.
• Bismuth: harmless black stool and black tongue — a classic distractor mistaken for melena.
• Tetracycline: photosensitivity; tooth discoloration in children.
• Levofloxacin: tendinopathy/rupture, aortic aneurysm risk, QT prolongation.
• Rifabutin: myelosuppression, orange discoloration of secretions, uveitis.
• Long-term PPI: hypomagnesemia, B12 and iron malabsorption, enteric infections, fundic gland polyps.

• ***Urease* is the signature enzyme: it splits urea into ammonia and CO2, buffering the periplasm and allowing survival at gastric pH. Two major tests flow directly from this mechanism — the urea breath test and the rapid urease test**. Separately, histology shows a curved/spiral gram-negative rod in the surface mucus layer on Giemsa or immunohistochemical staining — a morphologic clue, not a urease-based one.
• Best next step in a dyspeptic patient under 60 with no alarm features: noninvasive test-and-treat (urea breath test or stool antigen), not endoscopy. Alarm features (weight loss, dysphagia, vomiting, bleeding, anemia, age >60) mandate EGD first.
• The single most tested distractor: serology cannot be used for test of cure — IgG stays positive for years. Confirm eradication with urea breath test or stool antigen ≥4 weeks after therapy, with the PPI held ≥2 weeks.
• False negatives on urease-based tests occur with recent PPIs, antibiotics, bismuth, or active bleeding — the stem that says "patient on omeprazole with a negative breath test" wants you to hold the PPI and retest.
• First-line in the US is bismuth quadruple therapy (PPI + bismuth + tetracycline + metronidazole) per ACG, because clarithromycin resistance is high; clarithromycin triple is only for macrolide-naïve patients in low-resistance areas.
• The association examiners love: H. pylori → gastric MALT lymphoma, and eradication alone is the treatment for early-stage disease. Chemotherapy/radiation is the wrong first answer.
• Ulcer location logic: anterior duodenal ulcer → perforation with free air; posterior duodenal ulcer → hemorrhage from the gastroduodenal artery or penetration into the pancreas.
• Always biopsy a gastric ulcer to exclude adenocarcinoma; duodenal ulcers are essentially never malignant.
• Bismuth turns stool and tongue black — do not call it melena; check for anemia and occult blood before escalating.