Helicobacter pylori is a spiral-shaped bacterium that infects the stomach lining, and roughly 44% of adults worldwide currently carry it. You don’t “develop” it on your own. It’s acquired from other people or, less commonly, from contaminated water. The infection is almost always picked up in childhood, typically before age 10, and can persist for decades if untreated.
How H. pylori Spreads Between People
The bacterium passes from person to person through three main routes: contact with fecal matter (fecal-oral), contact with saliva or mouth secretions (oral-oral), and contact with vomit (gastric-oral). Of these, exposure to vomit from an infected person appears to be the single most efficient way the bacterium spreads. A CDC-supported study of households found that exposure to an infected family member who was vomiting increased the risk of new infection more than sixfold. That exposure alone accounted for over half of all new infections tracked in the study.
Diarrheal illness in an infected household member also raises risk, though less dramatically. The bacterium has been reliably recovered from both vomit and stool during episodes of gastroenteritis, which means ordinary stomach bugs can become opportunities for H. pylori to jump between family members. This is one reason infection clusters so strongly within households.
Contaminated Water and Environmental Sources
H. pylori has been detected in surface water, shallow groundwater, and well water. A U.S. study found the bacterium in a majority of surface water and shallow groundwater samples tested. It can also survive inside biofilms, the slimy layers that coat the interior of pipes and water storage tanks, which helps it persist in water systems even after basic treatment.
Drinking well water has been linked to higher infection rates in multiple studies. One German study found that people who regularly drank well water had roughly 2.3 times the odds of being infected compared to those who did not. In areas without treated municipal water, this becomes a significant route of exposure.
Why Living Conditions Matter So Much
H. pylori infection rates track closely with socioeconomic conditions. Crowded housing, limited sanitation, and lack of clean water are the strongest predictors of who gets infected and how early in life it happens. The number of children in a household and the number of people sharing a room are both independent risk factors. A German study found that having more than three children in the home more than doubled the odds of infection.
Other markers of poor living conditions, like unpaved roads, lack of sewage infrastructure, and limited access to handwashing, consistently show up in epidemiological research. One study found a direct link between less frequent handwashing and higher infection rates. These patterns explain why H. pylori prevalence is much higher in low- and middle-income countries and why rates have been declining globally as sanitation improves, from about 53% before 1990 to 44% in recent years.
How the Bacterium Survives in Your Stomach
Your stomach is one of the most hostile environments in the body, with acid strong enough to break down food and kill most bacteria. H. pylori has evolved a clever workaround. It produces enormous quantities of an enzyme called urease, which makes up about 10% of all the protein in the bacterial cell. This enzyme breaks down urea (a natural waste product present in gastric fluid) into ammonia and carbon dioxide. The ammonia neutralizes the acid immediately surrounding the bacterium, creating a small pocket of near-neutral pH where it can survive.
The system is self-regulating. When stomach acid increases, specialized channels in the bacterial membrane open wider to let more urea flood in, which produces more ammonia, which neutralizes more acid. The carbon dioxide byproduct gets converted into bicarbonate, another buffering agent, keeping the space around the bacterium at a steady pH of about 6.1, compared to the stomach’s normal pH of 1.5 to 3.5. This is why H. pylori can colonize a place where virtually no other bacterium can live, and why infections last for life without treatment.
Diet and Nutritional Factors
What you eat doesn’t cause H. pylori infection directly, but diet appears to influence whether the bacterium successfully colonizes and thrives once it arrives. High salt intake damages the protective mucus layer of the stomach, making it easier for H. pylori to take hold and trigger inflammation. Diets heavy in processed meats, soft drinks, and high-fat foods have been associated with higher infection rates. One study found significant correlations between frequent consumption of sausages, burgers, and soft drinks and active H. pylori infection.
On the protective side, regular intake of fresh fruits and vegetables, particularly tomatoes, onions, green peppers, apples, and citrus fruits, was associated with lower rates of infection. Fish, olive oil, honey, and legumes also showed protective associations. People with H. pylori infections tended to have lower intakes of vitamin C and folate compared to uninfected individuals, suggesting that these nutrients may help the stomach lining resist colonization.
Genetics and Family Susceptibility
Not everyone exposed to H. pylori develops the same outcomes. Genetics play a role in determining how your immune system responds to the infection and whether it progresses to ulcers or cancer. People with a family history of gastric disease have a higher relative risk of developing ulcers or gastritis when infected. Specific variations in genes that control inflammatory signaling molecules can increase the likelihood of a chronic, low-acid response to infection, which paradoxically makes the stomach more hospitable to the bacterium and raises the risk of gastric cancer over time.
Other genetic variants influence whether an infected person develops duodenal ulcers specifically. These aren’t genes that make you more likely to catch H. pylori. They determine what happens after you’re already infected, which is why two people in the same household can carry the same bacterium but have very different health outcomes.
Medical Equipment as a Rare Source
Endoscopes and biopsy instruments can carry H. pylori from one patient to the next if not properly disinfected. The bacterium readily contaminates equipment after examining an infected patient, and traditional cleaning with alcohol rinse is not sufficient to eliminate it. The estimated transmission rate is about 4 per 1,000 endoscopies when the infection rate in the patient population is around 60%. Modern disinfection protocols have largely addressed this risk, but it remains a documented route of transmission, particularly in settings where equipment sterilization standards are inconsistent.
Why It Matters
H. pylori is classified as a Group 1 carcinogen. It is the strongest known risk factor for stomach cancer, responsible for approximately 75% of all gastric cancer cases worldwide. Most carriers never develop cancer, but chronic infection drives a slow progression from inflammation to tissue changes that, in a subset of people, becomes malignant over decades. The infection is also the primary cause of peptic ulcers, which were historically blamed on stress and spicy food before the bacterium’s role was established in the 1980s.
The most effective prevention strategies are the simplest: thorough handwashing, drinking treated or boiled water, maintaining good oral hygiene, and avoiding shared utensils in households where someone is infected. Using serving utensils at meals rather than sharing dishes directly also reduces oral-oral transmission risk, particularly for young children who are most vulnerable to acquiring the infection.