H. pylori is one of the most common bacterial infections in the world. Roughly 44% of adults globally carry the bacterium, and in some regions that figure climbs well above 50%. Most people who are infected never realize it, living their entire lives without symptoms. But for a significant minority, the infection leads to ulcers or, over decades, stomach cancer.
Global and U.S. Prevalence
An analysis of data from 62 countries found a global H. pylori prevalence of 48%. A more recent review covering 2015 to 2022 put the figure at 44% in adults and 35% in children and adolescents. The infection is far more common in lower-income countries, where crowded living conditions and limited sanitation create ideal conditions for spread.
In the United States, rates are lower but still substantial. A large study of over 900,000 individuals in the Veterans Healthcare System found an overall positivity rate of 25.8%. The good news: that number has been dropping. Positivity fell from about 36% in 1999–2006 to 18.4% in 2013–2018, likely reflecting improvements in sanitation, smaller household sizes, and wider use of treatment.
Rates in the U.S. vary sharply by race and ethnicity. Black Americans had the highest positivity at around 40%, followed by Hispanic Americans at roughly 37%, compared with about 20% among white Americans. That gap has actually widened over time. In the most recent period studied, Black Americans were 2.4 times more likely to test positive than white Americans. Men tested positive slightly more often than women, and people over 60 had higher rates than younger adults.
Why Infection Rates Vary So Much
Socioeconomic status is one of the strongest predictors of H. pylori infection. A Japanese cross-sectional study of over 3,400 people found that those with high socioeconomic status were less than half as likely to be infected compared to those with low socioeconomic status. The connection is straightforward: lower income correlates with more crowded housing, less reliable water treatment, and sanitary conditions that favor transmission.
The number of siblings you grew up with also matters. In the same study, people who had five or more siblings were roughly 2.5 times more likely to carry H. pylori than those with two or fewer. Even after adjusting for other factors like age, smoking, and body weight, both socioeconomic status and household size remained significant predictors. This pattern fits with what researchers understand about how the bacterium spreads: close contact in childhood is the primary window for transmission.
How H. Pylori Spreads
H. pylori is almost always acquired during childhood, typically before age 10, and persists for life unless treated. The exact transmission route remains debated, but person-to-person spread within families is the dominant pattern. Three pathways are considered most likely: through contact with vomit or gastric fluids, through saliva, and through the fecal-oral route.
Mother-to-child transmission appears particularly common. The bacterium has been cultured from saliva and detected in dental plaque, meaning contaminated oral secretions can pass directly to an infant during feeding. Contact with vomit is another route, especially relevant in young children who are frequently ill. The bacterium survives well in gastric juice outside the body.
Water and food also play a role, particularly in developing countries. Children with external water supplies or those consuming raw vegetables irrigated with untreated sewage water show higher infection rates. Contaminated water likely acts both as a reservoir and as a vehicle for fecal-oral transmission.
Most Infections Cause No Symptoms
The vast majority of people with H. pylori never develop any noticeable problems. The bacterium colonizes the stomach lining and can persist there for decades without causing pain, nausea, or any digestive complaints. This is why so many people carry it without knowing.
Among those who are infected, the estimated lifetime risk of developing a peptic ulcer is about 20%. The lifetime risk of stomach cancer is considerably smaller, in the range of 1 to 2% overall. However, a detailed simulation study from Japan, where stomach cancer rates are among the highest in the world, found significantly elevated risks in the infected population: 17% for men and about 8% for women over a lifetime. By comparison, uninfected men in the same population had roughly a 1% risk and uninfected women about 0.5%. In other words, the infection multiplied stomach cancer risk by a factor of 15 to 17 in that population.
These numbers vary by country and depend heavily on other factors like diet, smoking, and the specific strain of H. pylori involved. But they illustrate why public health agencies in high-prevalence regions have increasingly moved toward screening and treatment programs.
How Infection Is Detected
Because most carriers have no symptoms, H. pylori is often discovered incidentally or through targeted screening. The two most common non-invasive tests are the urea breath test and the stool antigen test.
The urea breath test is the more accurate option. You drink a solution containing a special form of carbon, and if H. pylori is present in your stomach, it breaks down the solution in a way that can be measured in your breath about 15 to 30 minutes later. Studies show this test has a sensitivity of 97% and a specificity of 100%, meaning it catches nearly every infection and almost never gives a false positive.
The stool antigen test is simpler but less reliable, with a sensitivity of about 70% and a specificity of 94%. That means it misses roughly 3 in 10 infections. It’s still useful as a first-line screening tool, especially in settings where breath testing isn’t available.
When an upper endoscopy is performed for other reasons, tissue samples can be tested directly. Biopsy-based methods like histology reach 100% sensitivity, making them the gold standard. But endoscopy is invasive and isn’t used purely for H. pylori detection in most cases.
Age Patterns and the Cohort Effect
Older adults consistently test positive at higher rates than younger people. In a Welsh population study, prevalence jumped from about 30% in men aged 30 to 34 to over 59% in those 45 and older. This pattern shows up across countries and populations.
The explanation is partly what epidemiologists call a cohort effect. People born in earlier decades grew up in conditions with more crowding, less reliable sanitation, and no effective treatment for H. pylori. Since the infection is usually acquired in childhood and persists for life, these older cohorts carry the infections they picked up 40, 50, or 60 years ago. Younger generations, raised with cleaner water and smaller families, simply had less exposure. As these older cohorts age, overall prevalence in developed countries continues to decline, which is exactly the trend seen in the U.S. data.