H. pylori spreads primarily through direct contact with an infected person’s saliva, vomit, or stool, and through water or food contaminated with fecal matter. The bacterium infects roughly half the world’s population, with most people acquiring it during childhood from a family member. Understanding the specific routes helps explain why infection rates are so much higher in areas with crowded living conditions and unreliable water treatment.
Person-to-Person Contact Is the Main Route
The most common way H. pylori moves between people is within households, particularly from parent to child. A study published in Emerging Infectious Diseases tracked families over time and found that children under two had an annual infection rate of 21%, far higher than the 7% rate across all ages in the same households. Living in close quarters with someone who carries the bacterium is the single biggest risk factor.
Three pathways explain most person-to-person spread:
- Oral-oral: H. pylori lives in dental plaque and, to a lesser extent, saliva. Sharing utensils, pre-chewing food for a child, or any close mouth-to-mouth contact can transfer the bacterium. Detection rates in dental plaque vary widely across studies, from near zero to very high, but the mouth clearly acts as a reservoir that can re-seed the stomach even after treatment.
- Fecal-oral: The bacterium sheds in stool. If someone doesn’t wash their hands thoroughly after using the bathroom and then handles food or touches surfaces, they can pass H. pylori to others.
- Gastric-oral (through vomit): This route is surprisingly potent. A JAMA study found that every vomit sample from infected subjects grew H. pylori, often in high quantities. Vomit was so consistently loaded with the bacterium that researchers described it as difficult to imagine circumstances in which it wouldn’t be infectious. Even the air sampled during vomiting grew H. pylori in about 38% of subjects, though the aerosolized bacteria traveled less than 1.2 meters and dissipated within minutes.
That last point matters in real life. When a family member with H. pylori catches a stomach bug and vomits at home, the people caring for them face a meaningful risk. The same household study found that exposure to an infected person who was vomiting increased the risk of new infection more than sixfold. Vomiting exposure alone explained over half of all new infections tracked in the study and more than 70% of the most clearly confirmed cases.
Contaminated Water and Food
In regions with inadequate sanitation, water is a major vehicle for H. pylori. The bacterium survives for extended periods in water systems, especially when chlorine levels are low. Research from Peru found H. pylori in drinking water samples where free chlorine residual was between 0.02 and 0.12 mg/L, well below the levels needed to kill it. In its dormant form, H. pylori can persist in water at refrigerator temperatures for up to 26 months.
Food is another pathway. Raw vegetables irrigated or washed with contaminated water can carry the bacterium. A systematic review of food samples in Iran found H. pylori in about 11% of various foods, vegetables, and water tested. The bacterium can survive for several days on different food items kept at cold temperatures, including up to nine to twelve days in milk stored at 4°C. This means that in places where produce is washed in untreated water or where dairy hygiene is poor, food acts as a direct transmission route.
This water and food pathway is the main reason infection rates differ so dramatically between wealthy and lower-income countries. Overcrowding, low socioeconomic status, and limited access to clean water are consistently the strongest predictors of high infection rates in a community.
Medical Procedures
H. pylori can theoretically spread through improperly cleaned endoscopes, the flexible tubes used to examine the stomach. Studies have shown that up to 61% of endoscopes become contaminated with H. pylori after being used on an infected patient. However, according to the American Society for Gastrointestinal Endoscopy, standard cleaning and disinfection protocols are highly effective at eliminating the bacterium. The few documented cases of endoscopic transmission were traced to lapses in reprocessing guidelines or defective equipment, not to normal procedures. In a modern clinical setting with proper protocols, this route is essentially a non-issue.
Why the Mouth Matters for Reinfection
One detail that surprises many people is that even after successful antibiotic treatment for a stomach infection, H. pylori hiding in dental plaque can recolonize the stomach. The mouth serves as what researchers call an “extra-gastric reservoir.” This is one reason some patients test positive again after completing treatment. It also reinforces why oral hygiene plays a role not just in preventing initial infection but in keeping it from coming back.
Practical Steps to Reduce Your Risk
Because H. pylori spreads through routes shared by many other gut infections, the prevention strategies are straightforward. Thorough handwashing, especially before preparing food and after using the bathroom, is the most effective everyday measure. When traveling in areas with unreliable water systems, drinking only bottled or properly treated water and avoiding raw vegetables you didn’t wash yourself reduces exposure significantly.
Within households, the most actionable step is getting tested and treated if you have ongoing digestive symptoms. Completing the full course of antibiotics and acid-reducing medication maximizes your chance of clearing the infection and, just as importantly, prevents you from passing the bacterium to family members. If someone in your household is vomiting from a stomach illness, careful cleanup and handwashing afterward matters more than most people realize, given how effectively vomit spreads H. pylori in confined spaces.