H. pylori spreads from person to person, most often through contact with infected vomit, stool, or saliva. About 43% of the global population carries this stomach bacterium, and most people pick it up during childhood, typically before age 10. The infection can persist for decades without symptoms, which is part of why it spreads so easily within families and close living situations.
The Main Transmission Routes
There are three recognized pathways for H. pylori to move between people: fecal-oral (traces of infected stool reaching someone’s mouth), oral-oral (through saliva), and gastric-oral (through vomit). All three have strong biological and epidemiological evidence behind them, but vomiting appears to be the single biggest driver of household spread. A CDC study of families found that exposure to an infected household member who was vomiting increased the risk of new infection more than sixfold. Over 50% of all new infections in the study, and over 70% of the most clearly confirmed cases, were linked to vomit exposure.
The bacterium has been recovered most reliably from vomit and from stool during episodes of diarrhea or rapid gut transit. This means the risk of spreading H. pylori spikes during bouts of stomach illness, when the bacteria are being shed in larger quantities. But the oral-oral route matters too. H. pylori has been isolated from saliva and dental plaque, which helps explain why it can spread between family members even without a gastrointestinal illness triggering it.
Contaminated Water and Food
Beyond direct person-to-person contact, water and food contaminated with fecal matter can serve as a source of infection. This is especially relevant in regions with limited sanitation infrastructure. Studies have detected H. pylori in untreated water supplies, raw vegetables, unpasteurized milk, and other dairy products. A large review of food and water samples in one country found the bacterium present in about 11% of tested items. While the exact role of food and water in global transmission is still being mapped out, the pattern is clear: anywhere sanitation is poor, H. pylori rates climb.
Why Most Infections Happen in Childhood
H. pylori is overwhelmingly a childhood infection. A long-term study that followed people from infancy into their twenties found that the yearly rate of new infection was 2.1% in children aged 4 to 5 and 1.5% in children aged 7 to 9, but dropped to just 0.3% per year by the early twenties. The median age for becoming infected was 7.5 years.
Several factors explain why children are more vulnerable. Young kids have more hand-to-mouth contact, less consistent hygiene habits, and closer physical contact with caregivers and siblings. Their immune systems are also still developing. Once the bacterium establishes itself in the stomach lining during childhood, it can persist there for life if untreated, often without ever causing noticeable symptoms.
Risk Factors That Increase Your Chances
Living conditions play a major role in whether someone encounters H. pylori. A 2025 meta-analysis in Frontiers in Public Health identified household overcrowding as a statistically significant risk factor, raising the odds of infection by 38%. That makes intuitive sense: more people sharing bathrooms, kitchens, and sleeping spaces means more opportunities for the bacterium to pass between them.
Other factors that consistently point toward higher risk include unsafe drinking water, lower socioeconomic status, and lower educational attainment. These didn’t all reach statistical significance individually in the meta-analysis, but they all pushed in the same direction. The pattern is consistent worldwide: H. pylori thrives where sanitation, clean water access, and living space are limited. This is why infection rates in low-income countries can reach 70% or higher, while rates in high-income countries with better infrastructure tend to be significantly lower.
How H. Pylori Survives in Your Stomach
Your stomach is one of the harshest environments in the body, with a pH low enough to kill most bacteria. H. pylori gets around this with a clever chemical trick. It produces large amounts of an enzyme that breaks down urea (a natural compound in stomach fluid) into ammonia and carbon dioxide. The ammonia raises the pH in the bacteria’s immediate surroundings, creating a neutral pocket that shields it from the acid.
This same chemical reaction also solves a second problem. The thick mucus lining your stomach wall normally forms a stiff gel in acidic conditions, which would trap the bacteria in place. But as H. pylori raises the local pH, that gel softens into a liquid, allowing the bacterium to swim freely through it using its corkscrew-shaped body. It doesn’t bore through the mucus like a screw through a cork, as scientists once thought. It liquefies the mucus around itself and swims to the stomach wall, where it sets up a long-term colony.
How Infections Are Detected
Most people with H. pylori have no symptoms at all, so the infection is often discovered only when someone is being evaluated for persistent stomach pain, ulcers, or other digestive complaints. The most accurate noninvasive test is the urea breath test, which has a sensitivity of about 94%. You swallow a small amount of specially labeled urea, and if H. pylori is present, the enzyme it produces breaks down the urea and releases labeled carbon dioxide that can be measured in your breath.
Stool antigen testing is another common option, with a sensitivity around 83%. It works well in populations where H. pylori is less common and is easier to administer, particularly for children. Blood tests that look for antibodies to H. pylori also exist, but they can’t distinguish between a current infection and one your body cleared in the past, so they’re less useful for guiding treatment decisions.
Reducing Your Risk
Because H. pylori spreads through contaminated hands, food, water, and close contact with infected people, prevention comes down to basic hygiene measures. Thorough handwashing before eating and after using the bathroom is the most straightforward step. When traveling in areas with unreliable water treatment, drinking bottled or boiled water and avoiding raw vegetables washed in tap water reduces exposure.
Within households, the risk of spread drops when infected family members get tested and treated, particularly before the bacterium can pass to young children. If someone in your home has confirmed H. pylori and develops a stomach bug with vomiting, careful cleanup and disinfection of contaminated surfaces matters more than usual, given how efficiently the bacterium spreads through vomit. Eating more cruciferous vegetables like broccoli, cauliflower, and cabbage has also been associated with a protective effect, though the mechanism is less well established than the hygiene measures.