What Causes H. pylori Infection
H. pylori infection is caused by transmission of the bacterium Helicobacter pylori, primarily through person-to-person spread via oral-oral or fecal-oral routes, with most infections acquired during childhood, especially within families. 1
Transmission Routes
The bacterium spreads through several documented pathways:
Primary Routes
Person-to-person transmission is the predominant mode, occurring through:
Intrafamilial transmission is particularly important, as the infection clusters within families and is passed from parents to children or between siblings living in close contact 1, 2
Secondary Routes
- Waterborne transmission through fecal contamination of untreated water sources, particularly relevant in developing countries 2
- Iatrogenic transmission via contaminated endoscopes or pH probes (the only definitively proven mode) 2, 4
Risk Factors for Acquisition
Timing and Demographics
- Childhood acquisition is the critical period, with most infections occurring before age 10 in developing countries 1, 5
- In developed countries, childhood infection is now rare due to improved sanitation 4
Environmental and Socioeconomic Factors
The following conditions facilitate transmission 2, 3:
- Poor sanitation and hygiene practices
- Crowded or high-density living conditions
- Low socioeconomic status
- Inadequate access to clean water
- Food prepared under suboptimal conditions or exposed to contaminated water/soil
Geographic Variation
Prevalence varies dramatically by region 5, 6:
- Developing countries: 70-90% of population infected
- Developed countries: Much lower prevalence
- High-risk populations in developed countries include immigrants from high-prevalence regions (Central/South America, Caribbean, Eastern Europe, Asia) 1
The Human Reservoir
Humans are the principal and essentially only reservoir for H. pylori 2, 4. While the bacterium has been isolated in some domestic cats and nonhuman primates, these are not considered significant sources of human infection 2, 4.
Important Clinical Context
Once acquired, H. pylori persists for life if untreated 6. The infection causes chronic gastritis in all infected individuals, with approximately 17% lifetime risk of peptic ulcer and variable risk of gastric cancer depending on geographic location and host factors 1.
Common Pitfall
Do not assume environmental sources (soil, animals) are major transmission routes—the evidence consistently points to person-to-person spread as the dominant mechanism. Focus prevention efforts on improving sanitation, reducing household crowding, and screening/treating family members of infected individuals 1.