Merck Manual

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Helicobacter pylori Infection

(H. pylori Infection)


Nimish Vakil

, MD, University of Wisconsin School of Medicine and Public Health

Last full review/revision Mar 2020| Content last modified Mar 2020
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Helicobacter pylori (H. pylori) infection is a bacterial infection that causes stomach inflammation (gastritis), peptic ulcer disease, and certain types of stomach cancer.

  • The infection is caused by a type of bacteria called Helicobacter pylori (H. pylori).

  • When symptoms of H. pylori infection do occur, they include indigestion and pain or discomfort in the upper abdomen.

  • Doctors often base the diagnosis on the results of a breath test and an examination of the stomach using a flexible viewing tube (upper endoscopy).

  • Treatment is with antibiotics and a proton pump inhibitor.

Infection with Helicobacter pylori is the most common cause of gastritis and peptic ulcer disease worldwide. Infection is very common and increases with age. By age 60, about 50% of people are infected. However, recent studies show fewer young people are becoming infected with H. pylori. Infection is most common among blacks, Hispanics, and Asians.

H. pylori can be found in stool, saliva, and plaque on the teeth. H. pylori can be transmitted from person to person, especially if people who are infected do not thoroughly wash their hands after a bowel movement. Because people may also spread the bacteria through kissing or other close contact, infections tend to cluster in families and among people who live in nursing homes and other supervised facilities.

Did You Know...

  • Certain bacteria, called Helicobacter pylori, are the most common cause of gastritis and peptic ulcers.

H. pylori bacteria grow in the protective mucus layer of the stomach lining, where they are less exposed to the highly acidic juices produced by the stomach. Additionally, H. pylori produces ammonia, which helps protect it from stomach acid and enables it to disrupt and penetrate the mucus layer.

Complications of H. pylori infection

Virtually all people who have H. pylori infection have stomach inflammation (gastritis), which may affect the entire stomach or only the lower part (antrum). Infection can sometimes lead to erosive gastritis and perhaps even a stomach (gastric) ulcer.

H. pylori contributes to ulcer formation by increasing acid production, interfering with the stomach's normal defenses against stomach acid, and producing toxins.

Long-term infection with H. pylori increases the risk of stomach cancer.


Only 20% of people whose gastritis was caused by H. pylori infection develop symptoms or complications such as a peptic ulcer of the stomach or duodenum.

People who do develop symptoms resulting from H. pylori infection have those typical of gastritis, including indigestion and pain or discomfort in the upper abdomen.

Ulcers caused by H. pylori infection cause symptoms similar to ulcers caused by other disorders, including pain in the upper abdomen.


  • Tests of breath or stool

  • Sometimes upper endoscopy

H. pylori can be detected with tests that use breath or stool samples.

Sometimes doctors use a flexible viewing tube (endoscope) to do an upper endoscopy to obtain a sample (biopsy) of the stomach lining. The sample can be tested for H. pylori by several methods.


The likelihood that a peptic ulcer caused by H. pylori infection will return during the course of 3 years is greater than 50% in people who have not been treated with antibiotics. This percentage decreases to less than 10% in people who have been treated with antibiotics. In addition, treatment of H. pylori infection may heal ulcers that have resisted previous treatment.


  • Antibiotics and a proton pump inhibitor

  • After treatment, tests to confirm eradication of H. pylori infection

The most common treatments for H. pylori infection include a proton pump inhibitor to reduce stomach acid production, two antibiotics, and sometimes also bismuth subsalicylate to kill the infection. One of several proton pump inhibitors, lansoprazoleomeprazolepantoprazolerabeprazole, or esomeprazole, is given. These drugs may cause diarrhea, constipation, and headache. Several different antibiotics may be used, including amoxicillin, clarithromycin, metronidazole, and tetracycline. All of these antibiotics may alter taste and cause nausea, and amoxicillin, clarithromycin, and tetracycline may cause diarrhea. Bismuth subsalicylate may cause constipation and darkening of the tongue and stool.

Doctors typically confirm that treatment was successful by repeating breath or stool tests or endoscopy about 4 weeks after treatment is finished.

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