H. pylori (Helicobacter pylori) is a spiral-shaped bacterium that infects the stomach lining, and roughly half the world’s population carries it. Most people never know they have it. About 85% to 90% of those infected live without any symptoms at all. But in a significant minority, the infection causes chronic inflammation that can lead to stomach ulcers, and in rarer cases, stomach cancer.
How Common H. Pylori Infection Is
Global prevalence sits around 44% in adults and 35% in children and adolescents, based on data from 2015 to 2022. The rates vary dramatically by region. Africa has the highest prevalence at roughly 70%, while Oceania has the lowest at about 24%. In adults, infection rates have dropped by 16% over the past 30 years, likely due to improved sanitation and wider access to clean water. That same decline hasn’t been seen in children and adolescents.
Most people pick up the infection during childhood, and it persists for life unless treated. Living in crowded households, lacking reliable access to clean water, and growing up in regions with high overall prevalence are the biggest risk factors.
How the Bacteria Survives in Your Stomach
Your stomach is one of the most hostile environments in the body, with acid strong enough to break down food. H. pylori has an unusual trick for surviving there: it produces massive quantities of an enzyme called urease, which makes up about 10% of the bacterium’s total protein. Urease breaks down urea (a natural compound in your body) into ammonia and carbon dioxide. The ammonia neutralizes the acid immediately surrounding the bacterium, creating a small protective bubble that keeps the pH livable.
The carbon dioxide plays a role too. It reacts with water to form bicarbonate, which acts as a buffer and helps maintain conditions inside the bacterial cell at a stable, less acidic level. This system lets H. pylori burrow into the mucus layer that coats your stomach wall, where it sets up a long-term infection and triggers the chronic inflammation responsible for ulcers and other complications.
Symptoms Most People Experience
The majority of infected people have no symptoms whatsoever. When symptoms do appear, they typically reflect gastritis (inflammation of the stomach lining) or a developing ulcer. You might notice a burning or gnawing pain in your upper abdomen, especially when your stomach is empty. Bloating, nausea, frequent burping, and a loss of appetite are also common.
About 10% to 15% of people with H. pylori develop a peptic ulcer. Ulcer pain often worsens between meals or during the night and may temporarily improve after eating or taking an antacid. If an ulcer bleeds, you might see dark or tarry stools, or vomit material that looks like coffee grounds.
The Link to Stomach Cancer
Chronic H. pylori infection is the strongest known risk factor for stomach cancer. People with long-standing infections face an increased risk of adenocarcinoma in the main body of the stomach, and in parts of the world where stomach cancer is common (especially in Asia), the risk extends to cancer near the junction with the esophagus as well. The bacterium is also strongly tied to a rare type of stomach lymphoma called MALT lymphoma. Nearly all patients diagnosed with gastric MALT lymphoma show signs of H. pylori infection.
It’s worth keeping this in perspective. While the relative risk increase is significant, the vast majority of people with H. pylori never develop cancer. The progression from infection to cancer typically takes decades and involves other contributing factors like diet, smoking, and genetics. Still, this connection is a key reason doctors recommend treating the infection when it’s found.
How H. Pylori Spreads
The bacterium passes from person to person, most often through fecal-oral, oral-oral, or gastric-oral routes. In practical terms, that means contaminated water, close contact with an infected person’s saliva, or exposure to vomit. Research from the CDC found that living with someone who has H. pylori and experiences a stomach illness involving vomiting increases your risk of new infection by more than sixfold. Exposure to vomit from an infected household member accounted for over half of all new infections in one study.
Transmission tends to cluster in families, particularly during childhood. Good hand hygiene, access to clean drinking water, and careful cleanup after stomach illnesses in the household are the most practical ways to reduce spread.
Testing for H. Pylori
Several reliable tests exist, and they fall into two categories: those that require an endoscopy and those that don’t.
The most accurate non-invasive option is the urea breath test. You swallow a small capsule or drink containing a special form of urea. If H. pylori is present, the bacteria’s urease enzyme breaks down the urea and releases labeled carbon dioxide, which is detected in your breath. This test has a sensitivity of about 92% to 94%, meaning it correctly identifies the infection in the vast majority of cases.
A stool antigen test, which detects H. pylori proteins in a stool sample, is another common option with about 83% sensitivity. Blood antibody tests are available but less useful because they can stay positive long after the infection has been cleared, making it hard to distinguish a current infection from a past one.
One important detail: if you’re taking a proton pump inhibitor (a common acid-reducing medication), you need to stop it at least two weeks before testing. If you’ve recently taken antibiotics, you should wait at least four weeks. Both can suppress the bacteria enough to produce a false-negative result without actually clearing the infection.
How Treatment Works
H. pylori treatment involves a combination of antibiotics and acid-reducing medications taken together for 14 days. The current preferred approach for patients who haven’t been treated before uses four medications at once: an acid reducer, bismuth (the active ingredient in Pepto-Bismol), and two antibiotics. This combination, called bismuth quadruple therapy, is recommended when doctors don’t know which antibiotics the specific strain of bacteria is sensitive to.
The reason for this aggressive approach is antibiotic resistance. Globally, resistance rates to commonly used antibiotics like clarithromycin exceed 15% across Asia, Europe, and Oceania. Resistance to metronidazole and amoxicillin tops 15% on all five continents. Because of this, the American College of Gastroenterology now specifically recommends against the older three-drug regimen built around clarithromycin unless lab testing has confirmed the bacteria respond to it.
If the first round of treatment doesn’t work, doctors adjust the approach. An optimized version of the four-drug regimen is typically tried next, and alternative antibiotic combinations are available for patients who don’t respond. Treatment can feel burdensome since you’re taking multiple pills several times a day for two weeks, and side effects like nausea, a metallic taste, and diarrhea are common. But completing the full course is essential for clearing the infection.
Confirming the Infection Is Gone
After finishing treatment, you’ll need a follow-up test to confirm the bacteria have been eradicated. The same non-invasive tests used for initial diagnosis (breath test or stool antigen test) work well for this. The timing matters: you need to wait long enough after treatment for the medications to clear your system, following the same rules about stopping acid reducers at least two weeks before and allowing four weeks after antibiotics. Skipping this confirmation step is a common mistake, because incomplete eradication can allow the infection to bounce back and become harder to treat the second time around.