Causes and Risk Factors of H. Pylori Infection
Primary Transmission Routes
H. pylori is transmitted person-to-person, primarily through oral-oral or fecal-oral routes, with humans serving as the principal reservoir. 1
The bacterium spreads through:
- Oral-oral transmission via vomitus or saliva, with H. pylori DNA detected in saliva, dental plaque, and gastric juice 1
- Fecal-oral transmission through contaminated water or food, particularly in areas with poor sanitation 1
- Waterborne transmission from fecal contamination of untreated water sources, especially in developing countries 1
- Iatrogenic transmission following endoscopy procedures, which is the only definitively proven mode of transmission 1
Major Risk Factors
Socioeconomic and Environmental Factors
Poor living conditions during childhood represent the strongest risk factor for H. pylori acquisition. 2, 1
Key environmental determinants include:
- Low socioeconomic status and familial poverty, which is the main risk factor among children 2
- Crowded or high-density living conditions that facilitate transmission among household members 1
- Inadequate sanitation practices and poor hygiene standards 2, 1
- Contaminated food and water sources, particularly food prepared under suboptimal conditions or exposed to contaminated water or soil 1
Familial and Household Clustering
First-degree relatives of infected individuals have a 2-3 times increased risk of H. pylori infection, rising to 10-fold when multiple family members are affected. 3
- Intrafamilial transmission occurs readily within households, with person-to-person spread being the dominant mechanism 3
- Recurrent infection after eradication often results from ongoing intrafamilial exposure, necessitating testing and treatment of all household members 3
- First-degree relatives of gastric cancer patients warrant particular attention due to substantially elevated cancer risk 3
Geographic and Demographic Factors
H. pylori prevalence varies dramatically by geographic region, with higher rates in developing versus developed countries. 2, 1
- Geographic origin from high gastric cancer incidence regions increases risk 3
- Age-related acquisition occurs predominantly during childhood, with most infections established early in life 2, 1
- Race and ethnicity influence prevalence patterns, though this largely reflects socioeconomic disparities 1
- Immigration status from high-prevalence countries maintains elevated infection rates even after relocation 2
Nutritional and Dietary Factors
Inadequate nutritional status increases susceptibility to H. pylori infection. 1
- Low consumption of fruits and vegetables removes protective factors against infection 1
- Vitamin C deficiency reduces natural defenses, as adequate vitamin C intake appears protective 1
- Food contamination through poor preparation practices or exposure to contaminated water increases transmission risk 1
Important Clinical Considerations
Common Pitfalls
- Do not overlook household screening when treating an index patient, as concurrent treatment of all positive household members is necessary to break the transmission cycle 3
- Recognize that reinfection after successful eradication strongly suggests ongoing intrafamilial exposure requiring family testing 3
- Prioritize testing first-degree relatives of gastric cancer patients regardless of symptoms, given their substantially elevated cancer risk 3
Bacterial and Host Factors in Disease Progression
While the question asks about causes of infection rather than disease progression, it's worth noting that once infection occurs, bacterial virulence factors (particularly CagA and VacA) and host genetic factors influence disease severity, though these do not cause the initial infection itself. 4
The environmental factors that contribute to gastric cancer development are subordinate to the effect of H. pylori infection itself, with nutrition playing only a small contributing role in the absence of infection. 4