Helicobacter pylori (H. pylori) is a spiral-shaped bacterium that lives in the lining of the human stomach. Roughly 44% of the world’s adult population carries it, making it one of the most common chronic infections on Earth. Most people with H. pylori never develop symptoms, but for the 10% to 15% who do, the infection can cause painful ulcers and significantly raise the risk of stomach cancer.
How It Survives in Stomach Acid
The human stomach is one of the harshest environments in the body, with acid strong enough to dissolve metal. H. pylori has a remarkable workaround: it produces large amounts of an enzyme called urease, which breaks down urea (a natural compound found in the stomach) into ammonia and carbon dioxide. The ammonia neutralizes the acid in the bacteria’s immediate surroundings, creating a small pocket of near-neutral pH where it can thrive. The carbon dioxide adds a second layer of protection by converting into bicarbonate in the space just outside the bacterial cell wall, keeping the local pH around 6.1, close to neutral.
The bacterium also has physical adaptations for stomach life. It’s S-shaped, about the width of a red blood cell, and propels itself with a tuft of five to seven whip-like tails (flagella) at one end. These flagella let it burrow into the thick mucus layer that coats the stomach lining, where the acid is less intense and the bacterium can attach directly to cells.
How H. Pylori Spreads
H. pylori passes from person to person, most commonly through fecal-oral, oral-oral, or gastric-oral routes. In practical terms, that means contact with contaminated food, water, saliva, or vomit. The bacterium has been most reliably recovered from vomit and from stool during bouts of diarrhea.
Household transmission is a major driver. In one CDC-published study, exposure to an infected household member who had gastroenteritis raised the risk of new infection nearly fivefold. Vomiting was an even stronger risk factor than diarrhea alone, with exposure to vomit accounting for more than half of all new infections in the study. Crowded living conditions and poor sanitation amplify spread, which is why infection rates have dropped dramatically in countries that have improved water treatment and household hygiene over the past century.
Most people acquire H. pylori during childhood, and without treatment, it persists for life. The global prevalence has fallen from about 53% before 1990 to 44% in recent years among adults, but in children and adolescents the rate hasn’t dropped significantly in any world region, sitting around 35%.
Symptoms and Warning Signs
The majority of people carrying H. pylori have no symptoms at all. When the infection does cause problems, it’s typically because the bacterium has triggered inflammation in the stomach lining (gastritis) or caused a peptic ulcer. Common symptoms include:
- Burning or aching abdominal pain, often worse on an empty stomach
- Bloating and fullness, sometimes with difficulty drinking normal amounts of fluid
- Hunger pangs one to three hours after eating
- Mild nausea, sometimes relieved by vomiting
- Unexplained weight loss or loss of appetite
- Frequent burping
Some symptoms signal a more serious complication like a bleeding ulcer or intestinal blockage. Black, tarry, or bloody stools, vomiting blood or material that looks like coffee grounds, and sudden severe abdominal pain all require emergency medical attention.
The Link to Stomach Cancer
H. pylori infection is the single strongest risk factor for cancers that develop in the stomach. Epidemiological studies estimate that roughly 75% of gastric cancers are attributable to the infection. This doesn’t mean 75% of infected people get cancer. The vast majority never do. But chronic, untreated H. pylori infection causes decades of low-grade inflammation that, in a small percentage of people, gradually transforms stomach cells in ways that can become malignant. The risk is highest in people with certain strains of the bacterium, a family history of stomach cancer, or long-standing severe inflammation.
How the Infection Is Diagnosed
Doctors can test for H. pylori with or without an endoscopy. The two most common non-invasive options are a urea breath test and a stool antigen test, both highly accurate.
The urea breath test works by having you swallow a small amount of specially labeled urea. If H. pylori is present, its urease enzyme breaks down the urea and releases labeled carbon dioxide, which shows up in your breath. This test has about 96% sensitivity and 93% specificity under standard conditions, meaning it catches nearly all true infections and rarely gives false positives.
The stool antigen test detects H. pylori proteins in a stool sample, with roughly 94% sensitivity and 97% specificity. It’s particularly useful for confirming the infection is gone after treatment.
When an endoscopy is performed (usually because of concerning symptoms like bleeding), the doctor can take a small tissue sample and run a rapid urease test on it directly, or send it for examination under a microscope. These biopsy-based methods have specificity above 95% and sensitivity in the 85% to 95% range.
Treatment: Why It Takes Multiple Drugs
Clearing H. pylori requires a combination of antibiotics and a powerful acid-reducing medication, taken together for 14 days. A single antibiotic isn’t enough because the bacterium has become increasingly resistant to commonly used drugs. The current preferred first-line approach for patients who haven’t been treated before is a four-drug regimen that includes bismuth (the active ingredient in Pepto-Bismol), two antibiotics, and an acid-suppressing medication.
If that combination fails, doctors typically adjust based on which antibiotics were used previously. In some cases, susceptibility testing (checking which antibiotics the specific strain of bacteria responds to) guides the next round. Certain antibiotic combinations, particularly those containing clarithromycin or levofloxacin, are now reserved only for cases where lab testing confirms the bacteria isn’t resistant to them.
Growing Antibiotic Resistance
Antibiotic resistance is a real challenge in H. pylori treatment. Primary resistance to clarithromycin, once a cornerstone of therapy, runs as high as 34% in the Western Pacific region and 33% in the Eastern Mediterranean. Even in the Americas, where resistance is lower at around 10%, rates climb after a failed treatment course. Metronidazole resistance is even more widespread, exceeding 50% in parts of Southeast Asia and the Eastern Mediterranean. This resistance pattern is the main reason treatment guidelines have shifted away from older three-drug regimens toward bismuth-based four-drug combinations.
Confirming the Infection Is Gone
After completing treatment, you’ll need to wait at least four weeks before retesting to confirm the bacteria has been eliminated. If you’re taking acid-reducing medications or bismuth-containing products, you may need to stop them up to two weeks before the follow-up test, since these can interfere with accuracy. The same breath or stool tests used for initial diagnosis work well for confirming eradication. If the first treatment didn’t work, a second round with a different antibiotic combination is the next step.