Does Helicobacter pylori (H. pylori) only reside in the stomach or can it affect other parts of the body?

Helicobacter pylori Primarily Resides in the Stomach with Limited Extragastric Presence

Helicobacter pylori primarily colonizes the human stomach and does not typically establish significant infections in other parts of the body, though it can have systemic effects and is associated with certain extragastric manifestations. 1

Primary Location of H. pylori

• H. pylori has evolved to survive in the unique biological niche of the gastric lumen, where it can withstand the acidic environment through various adaptations, particularly its significant urease activity 2
• The bacterium specifically colonizes the mucous layer of the gastric epithelium, causing chronic active gastritis 1
• Humans are the principal reservoir for H. pylori, with the stomach being its primary habitat 3

Extragastric Associations of H. pylori

While H. pylori primarily lives in the stomach, it has been linked to several conditions outside the stomach:

Established Extragastric Associations

• Iron-deficiency anemia: Strong evidence (Level 1a, Grade A recommendation) links H. pylori to otherwise unexplained iron-deficiency anemia 1
• Idiopathic thrombocytopenic purpura (ITP): Evidence level 1b, Grade A recommendation supports H. pylori eradication in patients with ITP 1
• Vitamin B12 deficiency: Moderate evidence (Level 3b, Grade B recommendation) associates H. pylori with vitamin B12 deficiency 1
• Drug absorption issues: H. pylori infection impairs the absorption of certain medications, including thyroxine and l-dopa, with improved bioavailability following eradication treatment 1

Lymphatic System Involvement

• H. pylori accounts for approximately 50% of gastrointestinal non-Hodgkin's lymphoma cases, particularly mucosa-associated lymphoid tissue (MALT) lymphoma 1
• Early-stage (Lugano I/II) low-grade MALT lymphoma can be cured by H. pylori eradication in 60-80% of cases 1
• When the t(11,18) translocation is present, H. pylori eradication is usually ineffective, requiring alternative treatments 1

Transmission Routes

• Person-to-person transmission is the most likely mode, via either oral-oral route (through vomitus or saliva) or fecal-oral route 3
• Iatrogenic transmission following endoscopy is the only definitively proven mode of transmission 3
• Waterborne transmission due to fecal contamination may be an important source, especially in areas with untreated water 3

Clinical Implications

• H. pylori testing and eradication should be considered in patients with unexplained iron-deficiency anemia, ITP, or vitamin B12 deficiency 1
• For patients on thyroxine or l-dopa with absorption issues, H. pylori eradication may improve drug bioavailability 1
• Current evidence does not support a definitive causative association between H. pylori and other extragastric disorders, including cardiovascular and neurological disorders 1

Important Caveats

• The evidence linking H. pylori to extragastric manifestations is strongest for hematological disorders (iron-deficiency anemia, ITP) 1
• While H. pylori DNA has been detected in saliva, dental plaque, and feces, this represents shedding rather than active infection sites 3
• H. pylori eradication should be prioritized in patients with established gastric disease and those with the extragastric conditions mentioned above 1, 4

In conclusion, while H. pylori can have systemic effects and is associated with certain conditions outside the stomach, it primarily colonizes and causes disease within the gastric environment, with no substantial evidence of active infection in other body sites.