What Causes Gastritis
The two most common causes of gastritis are chronic Helicobacter pylori infection (the dominant etiology) and autoimmune mechanisms, with H. pylori being responsible for the vast majority of cases. 1
Primary Etiologies
Helicobacter pylori Infection
H. pylori is the leading cause of chronic gastritis worldwide. The evidence is compelling: patients with H. pylori infection have a 5-fold increased rate of developing atrophic gastritis compared to uninfected individuals (rate ratio 5.0,95% CI 3.1-8.3), while atrophic gastritis incidence remains very low (<1% annually) in those without the infection 1. This bacterium causes chronic inflammation without crossing the mucosal epithelium, instead provoking an immune reaction that, while unable to eradicate the organism, contributes significantly to mucosal damage 2.
The prevalence is particularly high in:
- Non-White racial/ethnic minority groups
- Early-generation immigrants from high-risk countries (Central and South America, Caribbean, Eastern Europe, Asia, India)
- Populations with lower socioeconomic status 1, 3
Autoimmune Gastritis
Autoimmune gastritis (AIG) is significantly less common, with an estimated prevalence of 0.5-2% 1. This form results from autoantibodies against parietal cells and intrinsic factor, combined with T-cell-mediated destruction of the gastric oxyntic mucosa 1.
Key characteristics of autoimmune gastritis:
- Predominantly affects women
- Increases with age
- Strongly associated with other autoimmune diseases (up to one-third of patients with autoimmune thyroid disease have AIG) 1
- Unlike H. pylori gastritis, racial and ethnic variation is not prominent 1
- Leads to corpus-predominant atrophy and eventual pernicious anemia (prevalence 0.15-1%) 1
Additional Risk Factors for Non-Autoimmune Gastritis
Beyond H. pylori, other contributing factors include 1:
- Advanced age
- Tobacco use
- High-salt diet
- Chronic bile acid reflux (possibly)
Less Common Causes
While H. pylori and autoimmunity dominate, other etiologies exist 4, 5:
Infectious causes:
- Cytomegalovirus (primarily in immunocompromised patients)
- Epstein-Barr virus
- Bacterial infections (phlegmonous gastritis, gastric tuberculosis, syphilis)
- Fungal infections (Candida albicans)
- Parasitic infections (anisakiasis from raw seafood)
Non-infectious causes:
- NSAIDs and other medications (causing chemical gastropathy with minimal inflammation)
- Bile reflux
- Inflammatory bowel disease (especially Crohn's disease)
- Allergic/eosinophilic gastritis
- Lymphocytic gastritis
- Granulomatous gastritis
Clinical Implications
Critical pitfall: Atrophic gastritis is typically asymptomatic and often goes undiagnosed, with inconsistent reporting on histopathology contributing to underdiagnosis 1. The estimated prevalence reaches up to 15% in US populations, yet many cases remain unrecognized until complications develop.
For patients with unexplained iron or vitamin B-12 deficiency, atrophic gastritis should be high in the differential diagnosis, regardless of etiology 1. This is particularly important for corpus-predominant disease, which directly impacts nutrient absorption.
The distinction between H. pylori-associated and autoimmune gastritis matters clinically: H. pylori gastritis is potentially reversible with eradication therapy 3, while autoimmune gastritis requires lifelong monitoring for nutritional deficiencies and neoplastic complications including type 1 gastric neuroendocrine tumors 1.