H. pylori spreads primarily from person to person, most often through contact with infected vomit, stool, or saliva. Nearly 44% of adults worldwide carry the bacterium, and most pick it up during childhood from a parent or close household member. The infection then persists for life unless treated.
Person-to-Person Spread
Three main pathways move H. pylori between people: fecal-oral (traces of infected stool reaching someone’s mouth), oral-oral (through saliva), and gastric-oral (through vomit). Of these, vomiting appears to be the most efficient route. A CDC-backed study of households found that when an infected person had a stomach illness with vomiting, other household members faced roughly a sixfold increased risk of picking up the infection. Diarrhea-only illness carried a lower, statistically insignificant risk by comparison.
This makes sense biologically. The bacterium has been most reliably recovered from vomit and from stool during episodes of rapid gut transit, like diarrhea. In everyday life, this means a child or adult with a stomach bug can shed large amounts of H. pylori into the environment, where other family members are exposed through contaminated hands, surfaces, or shared spaces like bathrooms.
Why Families Are the Main Source
Most H. pylori infections trace back to the family home. Research consistently shows that mothers are the most common source of a child’s infection, likely because of the close physical contact involved in feeding and caregiving. But DNA-based studies that can match exact bacterial strains between family members have also confirmed father-to-child transmission, suggesting that any close household contact matters, not just the primary caregiver.
Notably, child-to-child transmission outside the family appears to be uncommon. A Swedish study found no significant evidence that children spread the bacterium to unrelated peers at school or daycare. The household itself, with its shared food, water, bathrooms, and prolonged close contact, is the critical setting.
Water and Food Contamination
H. pylori can also behave like a waterborne or foodborne pathogen. Water and food contaminated with human feces are a recognized route of infection, particularly in regions where water treatment is inconsistent. Researchers have isolated the bacterium from vegetables, animal-derived foods, and untreated water supplies, with one large review finding H. pylori in about 11% of food and water samples tested in a high-prevalence country.
The bacterium doesn’t survive long in warm environments. At room temperature it lasts about two days, and less than a day above 40°C (104°F). But in cool, moist conditions, like refrigerated water, it can remain viable for up to two weeks. This means contaminated water stored at low temperatures or raw produce washed with untreated water can carry live bacteria long enough to cause infection.
Key Risk Factors
Certain living conditions dramatically increase your chances of encountering H. pylori:
- Crowded housing. The more people sharing a home, the more opportunities for the bacterium to pass between them, especially among young children.
- Unreliable clean water. Untreated or poorly treated water is a direct vehicle for the bacterium, and also makes effective handwashing harder.
- Living in a developing country. H. pylori prevalence is highest in regions of Africa, South America, and parts of Asia, where both crowding and limited water infrastructure are more common.
These factors explain the stark global divide in infection rates. In high-income countries with modern sanitation, prevalence has been declining for decades. In lower-income settings, rates remain high and have shown no significant drop in children and adolescents even in recent years.
When Infection Typically Happens
Most people acquire H. pylori in early childhood, usually before age 10. Children’s immune systems are less effective at clearing the bacterium, and their close physical contact with parents creates ample opportunity for transmission. Once established, H. pylori colonizes the stomach lining and persists indefinitely. Adults can also become infected, but new infections in adulthood are far less common.
This childhood window is why prevalence patterns tend to reflect the sanitation conditions a person grew up in rather than where they live now. An adult who grew up in a crowded household with limited clean water may carry the infection for decades without symptoms, only discovering it when a stomach ulcer or other complication develops.
How to Reduce Your Risk
Because H. pylori spreads through contaminated hands, food, and water, the most effective preventive measures are basic hygiene practices. Thorough handwashing before preparing or eating food is the single most important step. If you’re in an area where tap water quality is uncertain, drinking only treated or boiled water and avoiding raw produce washed in untreated water reduces exposure.
During stomach illnesses in your household, careful cleanup of vomit and thorough hand hygiene afterward can limit the burst of transmission that gastroenteritis events create. Since vomiting by an infected person is one of the highest-risk moments for household spread, treating those episodes with extra caution around shared surfaces and linens makes a meaningful difference.