When discussing cancer causes, we often think of genetics or lifestyle choices. However, certain infections can also lead to cancer. According to the American Association for Cancer Research, 13% of cancer cases worldwide—about 2.2 million annually—are linked to bacterial or viral infections. These include well-known viruses such as hepatitis B, hepatitis C, and human papillomavirus (HPV), the main cause of cervical cancer.

Surprisingly, the leading infectious cause of cancer globally is a lesser-known bacterium: Helicobacter pylori, or H. pylori. In 2018 alone, H. pylori was associated with an estimated 810,000 cancer cases—more than HPV and hepatitis B combined.

What is H. pylori and how does it cause cancer?

a common stomach infection
H. pylori is a type of bacteria that resides in the stomach. Around 30–40% of people in the United States are infected at some point.

ulcers and inflammation
This bacterium can lead to stomach ulcers and gastritis—an inflammation of the stomach lining. Over time, this inflammation may result in pre-cancerous changes, especially in individuals with certain genetic traits, lifestyle factors, or specific H. pylori strains.

linked cancers
H. pylori is strongly associated with two cancers:

  • MALT lymphoma, a type of non-Hodgkin lymphoma that affects the stomach

  • Gastric adenocarcinoma, the most common form of stomach cancer, accounting for up to 95% of cases

People infected with H. pylori face a two- to six-times greater risk of developing these cancers compared to those without the infection. However, only about 1–3% of infected individuals will develop cancer.

How do you get H. pylori?

unclear transmission
The exact method of H. pylori transmission is not fully understood, but it likely spreads through bodily fluids. The bacteria have been found in saliva, gastric fluids, vomit, and stool, suggesting that oral and fecal routes are possible.

common in childhood
Most people acquire the infection in early childhood, particularly in environments with poor sanitation, crowded housing, or limited access to clean water.

regional disparities
Infections are far more prevalent in low- and middle-income countries. Within the U.S., certain populations—such as Indigenous American communities—have higher infection rates. For example:

  • 62% of Navajo adults in Arizona are infected

  • 75% of Alaska Natives carry the bacteria

Globally, gastric cancer rates are highest in East Asia, Eastern Europe, and parts of Latin America. In countries with high incidence, routine screening for gastric cancer is recommended beginning at age 40 or 50.

Symptoms and diagnosis

often asymptomatic
Many people with H. pylori don’t show any signs. Others may experience digestive discomfort, especially after eating.

severe symptoms
Advanced signs may include:

  • Vomiting

  • Weight loss

  • Difficulty swallowing

  • Severe heartburn

  • Black, foul-smelling stools (a sign of bleeding ulcers)

testing methods
To detect H. pylori, healthcare providers may use:

  • Urea breath test

  • Stool antigen test

  • Upper endoscopy

  • Blood test (less common in the U.S.)

Universal screening is not recommended in the U.S., but testing is advised for those who:

  • Show symptoms of infection

  • Have or had peptic ulcers

  • Live with someone who has H. pylori

  • Have a family history of gastric cancer or ulcers

  • Have MALT lymphoma or iron deficiency anemia

  • Take NSAIDs regularly

Treatment

challenging due to resistance
H. pylori infections usually don’t resolve without treatment and have become more difficult to treat because of increasing antibiotic resistance.

current regimens
Treatment typically includes a two-week course of multiple medications:

  • Proton pump inhibitors or other acid-suppressors

  • Two or more antibiotics

  • Sometimes bismuth compounds (like Pepto-Bismol)

In some cases, a second or third course of antibiotics is needed to clear the infection. Resistance testing exists but is not widely available in the U.S.

How to prevent an H. pylori infection

early prevention is difficult
Since the infection is commonly acquired during childhood, prevention is not always straightforward.

household transmission
Sharing rooms and household contact increases transmission risk. While giving siblings separate rooms may help, it’s not always practical—and having an infected family member is often a stronger predictor.

general precautions
To help reduce the spread:

  • Wash hands frequently, especially after using the restroom

  • Avoid sharing eating utensils and drinking containers

  • Drink water from clean, reliable sources

A quick review

H. pylori is the leading infectious cause of cancer worldwide and is highly prevalent globally. Although many people live with the bacteria without issues, it can cause ulcers and lead to stomach cancer in rare cases.

If you experience ongoing digestive discomfort or have risk factors, consult your healthcare provider. Testing and treatment can reduce the risk of complications—including serious outcomes like gastric cancer.