H. pylori spreads primarily from person to person, most often within families and households. The bacterium lives in the stomach lining and reaches new hosts through contact with infected vomit, stool, or saliva. About 43% of the global population carries H. pylori, and most people pick it up during early childhood from a family member.
Person-to-Person Contact Is the Main Route
H. pylori passes between people through three overlapping pathways: fecal-oral (when traces of infected stool reach someone’s mouth, usually via contaminated hands or surfaces), oral-oral (through saliva), and gastric-oral (through vomit). Of these, exposure to vomit from an infected person appears to be the single most important driver of new infections.
A CDC-published study tracking households over time found that 75% of new infections could be traced back to living with an infected person who had a stomach illness. Vomiting, specifically, was the bigger culprit: living with an infected household member who vomited raised the risk of a new infection more than sixfold. Diarrhea alone carried a smaller, less certain risk. Overall, exposure to an infected person’s vomit explained more than half of all new infections in the study and over 70% of the most clearly confirmed cases.
Children Are Most Vulnerable
Most H. pylori infections are acquired in early childhood, typically before age five. Young children are especially susceptible because of their developing immune systems, close physical contact with caregivers, and habits like putting hands and objects in their mouths. In the same household study, the annual infection rate for children under two was 21%, compared to 7% overall. The source is almost always a parent, sibling, or other household member who carries the bacterium, often without knowing it.
Once acquired in childhood, H. pylori typically persists for life unless treated. Many carriers never develop symptoms, which means the infection quietly circulates within families for years.
Contaminated Water and Food
H. pylori can survive outside the human body long enough to spread through water and food, particularly in areas with limited sanitation. The bacterium has been detected in freshwater sources, well water, and seawater, where it exists both free-floating and attached to tiny aquatic organisms.
On food, survival times vary but are long enough to matter. In laboratory studies, H. pylori survived up to 6 days on spinach, 3 to 5 days on lettuce and carrots depending on storage conditions, and 7 days in fermented sausage. In contaminated milk stored in a refrigerator, the bacterium persisted for 5 to 12 days depending on the type of milk. Shellfish are another potential vehicle: the bacterium survived for 6 days in contaminated mussels, spending the first 2 days in an actively growing state and the remaining 4 in a dormant but still viable form.
These findings help explain why regions with unsafe drinking water and less reliable food hygiene have consistently higher infection rates. Poor drinking water sources are associated with roughly a 35% increased risk of carrying H. pylori.
Crowded Living Conditions Increase Risk
Because H. pylori spreads through close contact and shared environments, the conditions you live in strongly influence your odds of infection. A large meta-analysis of social determinants identified household overcrowding as a significant risk factor, raising the likelihood of infection by 38%. This makes intuitive sense: more people sharing bathrooms, kitchens, and sleeping spaces means more opportunities for the bacterium to pass between family members.
Educational attainment showed a striking gradient. People with the lowest levels of formal education had roughly 3.5 times the infection risk compared to those with the highest, likely reflecting a cluster of related factors: income, housing quality, access to clean water, and health literacy. Occupational instability, a marker for economic precariousness, also increased risk by about 23%.
These patterns explain why global prevalence has been declining over time. As sanitation, housing, and living standards improve, fewer children encounter the bacterium early in life. Global prevalence dropped from an estimated 58% in the 1980s to about 43% in recent years, though rates still vary enormously between and within countries.
Can You Get It From Pets?
H. pylori strains have been found in dogs, cats, pigs, and some primates, raising the question of whether pets can pass the infection to their owners. The evidence so far is inconclusive. While the bacterium can colonize the stomachs of various animals, it remains unclear whether these animals carry it naturally or acquired it from human contact. Captive macaques, for instance, have tested positive for H. pylori, but researchers suspect they may have picked it up from human handlers rather than the other way around. For now, person-to-person transmission within households remains far more relevant than any animal source.
Practical Ways to Reduce Spread
Since the bacterium travels through stool, vomit, and saliva, the most effective prevention measures center on basic hygiene. Thorough handwashing, particularly before preparing or eating food and after using the bathroom, reduces the chance of fecal-oral transmission. If someone in your household has a stomach illness and is known to carry H. pylori, careful cleanup of vomit and avoidance of shared utensils during the illness can meaningfully lower risk to others in the home.
Food safety practices also help. Washing produce, cooking shellfish thoroughly, and ensuring that anyone handling food has clean hands all reduce the chance of picking up the bacterium from contaminated items. In areas where tap water quality is uncertain, using treated or boiled water for drinking and food preparation adds another layer of protection.
Perhaps the most impactful step at the household level is testing and treating infected family members, especially when one person has been diagnosed. Because carriers often have no symptoms, the infection can silently re-spread within a family even after one member is successfully treated. Identifying and treating the whole reservoir breaks the cycle.